rofi-menugen: convert patchPhase to postPatch, cleanup version

pkgs/applications/misc/rofi-menugen/default.nix

···
 { lib, stdenv, fetchFromGitHub, rofi, gnused }:
 
 stdenv.mkDerivation rec {
-  rev = "168efd2608fdb88b1aff3e0244bda8402169f207";
   pname = "rofi-menugen";
-  version = "unstable-2015-12-28-${builtins.substring 0 7 rev}";
+  version = "unstable-2015-12-28";
 
   src = fetchFromGitHub {
     owner = "octotep";
     repo = "menugen";
-    inherit rev;
+    rev = "168efd2608fdb88b1aff3e0244bda8402169f207";
     sha256 = "09fk9i6crw772qlc5zld35pcff1jq4jcag0syial2q000fbpjx5m";
   };
-  patchPhase = ''
+
+  postPatch = ''
     sed -i -e "s|menugenbase|$out/bin/rofi-menugenbase|" menugen
     sed -i -e "s|rofi |${rofi}/bin/rofi |" menugen
     sed -i -e "s|sed |${gnused}/bin/sed |" menugenbase
   '';
+
   installPhase = ''
     mkdir -p $out/bin
     cp menugen $out/bin/rofi-menugen
     cp menugenbase $out/bin/rofi-menugenbase
   '';
+
   meta = with lib; {
     description = "Generates menu based applications using rofi";
     homepage = "https://github.com/octotep/menugen";