gnu: expat: Update replacement to 2.2.2 [security fixes].

See 'Changes' in the source distribution for more information about the
fixed security issues.

* gnu/packages/xml.scm (expat)[replacement]: Update to 2.2.2.
(expat-2.2.1): Replace with ...
(expat-2.2.2): ... new variable.

gnu/packages/xml.scm

@@ -56,7 +56,7 @@
   (package
     (name "expat")
     (version "2.2.0")
-    (replacement expat-2.2.1)
+    (replacement expat-2.2.2)
     (source (origin
              (method url-fetch)
              (uri (string-append "mirror://sourceforge/expat/expat/"
@@ -75,17 +75,17 @@ stream-oriented parser in which an application registers handlers for
 things the parser might find in the XML document (like start tags).")
     (license license:expat)))
 
-(define expat-2.2.1  ; Fixes CVE-2017-9233, CVE-2016-9063 and other issues.
+(define expat-2.2.2  ; Fixes CVE-2017-9233, CVE-2016-9063 and other issues.
   (package
     (inherit expat)
-    (version "2.2.1")
+    (version "2.2.2")
     (source (origin
              (method url-fetch)
              (uri (string-append "mirror://sourceforge/expat/expat/"
                                  version "/expat-" version ".tar.bz2"))
              (sha256
               (base32
-               "11c8jy1wvllvlk7xdc5cm8hdhg0hvs8j0aqy6s702an8wkdcls0q"))))))
+               "0ik0r39ala9c6hj4kxrk933klgwkzlkbrfhvhaykx8l1rwgr2xj3"))))))
 
 (define-public libebml
   (package