gnu: gtk+: Update to 3.20.2.

* gnu/packages/gtk.scm (gtk+): Update to 3.20.2.

gnu/packages/gtk.scm

@@ -606,7 +606,7 @@ application suites.")
 (define-public gtk+
   (package (inherit gtk+-2)
    (name "gtk+")
-   (version "3.18.2")
+   (version "3.20.2")
    (source (origin
             (method url-fetch)
             (uri (string-append "mirror://gnome/sources/" name "/"
@@ -614,7 +614,7 @@ application suites.")
                                 name "-" version ".tar.xz"))
             (sha256
              (base32
-              "0lp1hn0qydxx03bianzzr0a4maqzsvylrkzr7c3p0050qihwbgjx"))
+              "1xv97zrngf47hyrxz7rfrdl5xpv4y61rkmipyi300pm5iq3d3c8s"))
             (patches (search-patches "gtk3-respect-GUIX_GTK3_PATH.patch"))))
    (propagated-inputs
     `(("at-spi2-atk" ,at-spi2-atk)