gmime: update from 2.6.19 to 2.6.20

pkgs/development/libraries/gmime/default.nix

···
 { stdenv, fetchurl, pkgconfig, glib, zlib, libgpgerror }:
 
 stdenv.mkDerivation rec {
-  name = "gmime-2.6.19";
+  name = "gmime-2.6.20";
 
   src = fetchurl {
     url = "mirror://gnome/sources/gmime/2.6/${name}.tar.xz";
-    sha256 = "0jm1fgbjgh496rsc0il2y46qd4bqq2ln9168p4zzh68mk4ml1yxg";
+    sha256 = "0rfzbgsh8ira5p76kdghygl5i3fvmmx4wbw5rp7f8ajc4vxp18g0";
   };
 
   nativeBuildInputs = [ pkgconfig ];