Fix issues raised at review

The issues can be found at https://github.com/NixOS/nixpkgs/pull/227295.
The review was quite helpful.

pkgs/applications/version-management/git-cache/default.nix

@@ -1,6 +1,6 @@
 {fetchFromGitHub, lib, stdenv}:
 
-stdenv.mkDerivation rec {
+stdenv.mkDerivation {
   pname = "git-cache";
   version = "2018-06-18";
 
@@ -8,7 +8,7 @@ stdenv.mkDerivation rec {
     owner = "Seb35";
     repo = "git-cache";
     rev = "354f661e40b358c5916c06957bd6b2c65426f452";
-    sha256 = "sha256-V7rQOy+s9Lzdc+RTA2QGPfyavw4De/qQ+tWrzYtO2qA=";
+    hash = "sha256-V7rQOy+s9Lzdc+RTA2QGPfyavw4De/qQ+tWrzYtO2qA=";
   };
 
   dontBuild = true;
@@ -19,9 +19,9 @@ stdenv.mkDerivation rec {
 
   meta = with lib; {
     homepage = "https://github.com/Seb35/git-cache";
-    license = lib.licenses.wtfpl;
+    license = licenses.wtfpl;
     description = "A program to add and manage a system-wide or user-wide cache for remote git repositories";
-    platforms = with platforms; linux ++ darwin;
-    maintainers = [];
+    platforms = platforms.unix;
+    maintainers = with maintainers; [ maxhearnden ];
   };
 }