doc: Use HTTPS for external links.

* doc/contributing.texi
  (14.1 Building from Git,
   14.3 The Perfect Setup,
   14.4.1 Software Freedom,
   14.4.4 Synopses and Descriptions,
   14.5.4 Formatting Code):
   Use HTTPS for @uref{}s and @url{}s that support it.

* doc/fdl-1.3.texi
  (Appendix A GNU Free Documentation License):
  Use HTTPS for @uref{}s and @url{}s that support it.

* doc/guix.texi
  (6.3 Build Systems,
   8.8.4 Networking Services,
   8.8.8 Sound Services,
   8.8.16 Web Services,
   8.11 Name Service Switch,
   12.2 Preparing to Use the Bootstrap Binaries);
   Use HTTPS for @uref{}s and @url{}s that support it.

Signed-off-by: Marius Bakke <mbakke@fastmail.com>

doc/contributing.texi

@@ -98,12 +98,12 @@ following are the required packages in addition to those mentioned in the
 installation instructions (@pxref{Requirements}).
 
 @itemize
-@item @url{http://gnu.org/software/autoconf/, GNU Autoconf};
-@item @url{http://gnu.org/software/automake/, GNU Automake};
-@item @url{http://gnu.org/software/gettext/, GNU Gettext};
-@item @url{http://gnu.org/software/texinfo/, GNU Texinfo};
-@item @url{http://www.graphviz.org/, Graphviz};
-@item @url{http://www.gnu.org/software/help2man/, GNU Help2man (optional)}.
+@item @url{https://gnu.org/software/autoconf/, GNU Autoconf};
+@item @url{https://gnu.org/software/automake/, GNU Automake};
+@item @url{https://gnu.org/software/gettext/, GNU Gettext};
+@item @url{https://gnu.org/software/texinfo/, GNU Texinfo};
+@item @url{https://www.graphviz.org/, Graphviz};
+@item @url{https://www.gnu.org/software/help2man/, GNU Help2man (optional)}.
 @end itemize
 
 On Guix, extra dependencies can be added by instead running @command{guix
@@ -217,8 +217,8 @@ you want to upgrade your local source tree.
 The Perfect Setup to hack on Guix is basically the perfect setup used
 for Guile hacking (@pxref{Using Guile in Emacs,,, guile, Guile Reference
 Manual}).  First, you need more than an editor, you need
-@url{http://www.gnu.org/software/emacs, Emacs}, empowered by the
-wonderful @url{http://nongnu.org/geiser/, Geiser}.  To set that up, run:
+@url{https://www.gnu.org/software/emacs, Emacs}, empowered by the
+wonderful @url{https://nongnu.org/geiser/, Geiser}.  To set that up, run:
 
 @example
 guix package -i emacs guile emacs-geiser
@@ -250,7 +250,7 @@ s-expression, etc.
 @cindex reducing boilerplate
 We also provide templates for common git commit messages and package
 definitions in the @file{etc/snippets} directory.  These templates can
-be used with @url{http://joaotavora.github.io/yasnippet/, YASnippet} to
+be used with @url{https://joaotavora.github.io/yasnippet/, YASnippet} to
 expand short trigger strings to interactive text snippets.  You may want
 to add the snippets directory to the @var{yas-snippet-dirs} variable in
 Emacs.
@@ -385,14 +385,14 @@ needed is to review and apply the patch.
 @cindex free software
 The GNU operating system has been developed so that users can have
 freedom in their computing.  GNU is @dfn{free software}, meaning that
-users have the @url{http://www.gnu.org/philosophy/free-sw.html,four
+users have the @url{https://www.gnu.org/philosophy/free-sw.html,four
 essential freedoms}: to run the program, to study and change the program
 in source code form, to redistribute exact copies, and to distribute
 modified versions.  Packages found in the GNU distribution provide only
 software that conveys these four freedoms.
 
 In addition, the GNU distribution follow the
-@url{http://www.gnu.org/distros/free-system-distribution-guidelines.html,free
+@url{https://www.gnu.org/distros/free-system-distribution-guidelines.html,free
 software distribution guidelines}.  Among other things, these guidelines
 reject non-free firmware, recommendations of non-free software, and
 discuss ways to deal with trademarks and patents.
@@ -571,7 +571,7 @@ such as @command{guix package --show} take care of rendering it
 appropriately.
 
 Synopses and descriptions are translated by volunteers
-@uref{http://translationproject.org/domain/guix-packages.html, at the
+@uref{https://translationproject.org/domain/guix-packages.html, at the
 Translation Project} so that as many users as possible can read them in
 their native language.  User interfaces search them and display them in
 the language specified by the current locale.
@@ -838,7 +838,7 @@ especially when matching lists.
 @cindex coding style
 When writing Scheme code, we follow common wisdom among Scheme
 programmers.  In general, we follow the
-@url{http://mumble.net/~campbell/scheme/style.txt, Riastradh's Lisp
+@url{https://mumble.net/~campbell/scheme/style.txt, Riastradh's Lisp
 Style Rules}.  This document happens to describe the conventions mostly
 used in Guile’s code too.  It is very thoughtful and well written, so
 please do read it.

doc/fdl-1.3.texi

@@ -6,7 +6,7 @@
 
 @display
 Copyright @copyright{} 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
-@uref{http://fsf.org/}
+@uref{https://fsf.org/}
 
 Everyone is permitted to copy and distribute verbatim copies
 of this license document, but changing it is not allowed.
@@ -414,7 +414,7 @@ The Free Software Foundation may publish new, revised versions
 of the GNU Free Documentation License from time to time.  Such new
 versions will be similar in spirit to the present version, but may
 differ in detail to address new problems or concerns.  See
-@uref{http://www.gnu.org/copyleft/}.
+@uref{https://www.gnu.org/copyleft/}.
 
 Each version of the License is given a distinguishing version number.
 If the Document specifies that a particular numbered version of this

doc/guix.texi

@@ -6778,7 +6778,7 @@ linux-module-build-system, use the key #:linux to specify it).
 
 @defvr {Scheme Variable} node-build-system
 This variable is exported by @code{(guix build-system node)}.  It
-implements the build procedure used by @uref{http://nodejs.org,
+implements the build procedure used by @uref{https://nodejs.org,
 Node.js}, which implements an approximation of the @code{npm install}
 command, followed by an @code{npm test} command.
 
@@ -13351,7 +13351,7 @@ The ModemManager package to use.
 
 @defvr {Scheme Variable} usb-modeswitch-service-type
 This is the service type for the
-@uref{http://www.draisberghof.de/usb_modeswitch/, USB_ModeSwitch} service. The
+@uref{https://www.draisberghof.de/usb_modeswitch/, USB_ModeSwitch} service. The
 value for this service type is a @code{usb-modeswitch-configuration} record.
 
 When plugged in, some USB modems (and other USB devices) initially present
@@ -13596,7 +13596,7 @@ The nftables ruleset to use.  This may be any ``file-like'' object
 @cindex ntpd, service for the Network Time Protocol daemon
 @cindex real time clock
 @defvr {Scheme Variable} ntp-service-type
-This is the type of the service running the @uref{http://www.ntp.org,
+This is the type of the service running the @uref{https://www.ntp.org,
 Network Time Protocol (NTP)} daemon, @command{ntpd}.  The daemon will keep the
 system clock synchronized with that of the specified NTP servers.
 
@@ -14234,7 +14234,7 @@ Its value must be a @code{zero-configuration} record---see below.
 
 This service extends the name service cache daemon (nscd) so that it can
 resolve @code{.local} host names using
-@uref{http://0pointer.de/lennart/projects/nss-mdns/, nss-mdns}.  @xref{Name
+@uref{https://0pointer.de/lennart/projects/nss-mdns/, nss-mdns}.  @xref{Name
 Service Switch}, for information on host name resolution.
 
 Additionally, add the @var{avahi} package to the system profile so that
@@ -16053,7 +16053,7 @@ Data type representing the configuration for @code{alsa-service}.
 
 @item @code{pulseaudio?} (default: @var{#t})
 Whether ALSA applications should transparently be made to use the
-@uref{http://www.pulseaudio.org/, PulseAudio} sound server.
+@uref{https://www.pulseaudio.org/, PulseAudio} sound server.
 
 Using PulseAudio allows you to run several sound-producing applications
 at the same time and to individual control them @i{via}
@@ -16101,7 +16101,7 @@ See @uref{https://www.alsa-project.org/main/index.php/Asoundrc} for the
 details.
 
 @deffn {Scheme Variable} pulseaudio-service-type
-This is the type for the  @uref{http://www.pulseaudio.org/, PulseAudio}
+This is the type for the  @uref{https://www.pulseaudio.org/, PulseAudio}
 sound server.  It exists to allow system overrides of the default settings
 via @code{pulseaudio-configuration}, see below.
 
@@ -20399,7 +20399,7 @@ configuration.  Otherwise this must be a file-like object with valid
 VCL syntax.
 
 @c Varnish does not support HTTPS, so keep this URL to avoid confusion.
-For example, to mirror @url{http://www.gnu.org,www.gnu.org} with VCL you
+For example, to mirror @url{https://www.gnu.org,www.gnu.org} with VCL you
 can do something along these lines:
 
 @lisp
@@ -25828,7 +25828,7 @@ next method in the list.  The NSS configuration is given in the
 @cindex nss-mdns
 @cindex .local, host name lookup
 As an example, the declaration below configures the NSS to use the
-@uref{http://0pointer.de/lennart/projects/nss-mdns/, @code{nss-mdns}
+@uref{https://0pointer.de/lennart/projects/nss-mdns/, @code{nss-mdns}
 back-end}, which supports host name lookups over multicast DNS (mDNS)
 for host names ending in @code{.local}:
 
@@ -28300,7 +28300,7 @@ transparency that we get in the rest of the package dependency graph,
 where Guix always gives us a source-to-binary mapping.  Thus, our goal
 is to reduce the set of bootstrap binaries to the bare minimum.
 
-The @uref{http://bootstrappable.org, Bootstrappable.org web site} lists
+The @uref{https://bootstrappable.org, Bootstrappable.org web site} lists
 on-going projects to do that.  One of these is about replacing the
 bootstrap GCC with a sequence of assemblers, interpreters, and compilers
 of increasing complexity, which could be built from source starting from