cataclysm-dda-git: differentiate the version display from 0.C

Previously the version shown in the title was 0.C, not distinguishable
from the stable version.

pkgs/games/cataclysm-dda/git.nix

@@ -26,6 +26,7 @@ stdenv.mkDerivation rec {
   makeFlags = [
     "PREFIX=$(out) LUA=1 TILES=1 SOUND=1 RELEASE=1 USE_HOME_DIR=1"
     "LANGUAGES=all"
+    "VERSION=git-${version}-${stdenv.lib.substring 0 8 src.rev}"
   ] ++ stdenv.lib.optionals stdenv.isDarwin [
     "NATIVE=osx CLANG=1"
   ];