add git repositry and meta.branch

pkgs/applications/misc/mupdf/default.nix

···
 
   meta = {
     homepage = http://mupdf.com/;
+    repositories.git = git://git.ghostscript.com/mupdf.git;
     description = "Lightweight PDF viewer and toolkit written in portable C";
     license = "GPLv3+";
     maintainers = with stdenv.lib.maintainers; [ viric ];

pkgs/development/libraries/giflib/4.1.nix

···
     url = mirror://sourceforge/giflib/giflib-4.1.6.tar.bz2;
     sha256 = "1v9b7ywz7qg8hli0s9vv1b8q9xxb2xvqq2mg1zpr73xwqpcwxhg1";
   };
+  meta = {
+    branch = "4.1";
+  };
 }