graphite-cursors: replace "${version}" with version

pkgs/data/icons/graphite-cursors/default.nix

···
   src = fetchFromGitHub {
     owner = "vinceliuice";
     repo = pname;
-    rev = "${version}";
+    rev = version;
     sha256 = "sha256-Kopl2NweYrq9rhw+0EUMhY/pfGo4g387927TZAhI5/A=";
   };