treewide: simplify rev/repo arguments in src

+ use fetchFromGithub where possible

pkgs/games/the-butterfly-effect/default.nix

@@ -1,11 +1,12 @@
-{ stdenv, mkDerivation, fetchgit, qt5, box2d, which, cmake, gettext }:
+{ stdenv, mkDerivation, fetchFromGitHub, qt5, box2d, which, cmake, gettext }:
 
 mkDerivation rec {
   pname = "tbe";
   version = "0.9.3.1";
 
-  src = fetchgit {
-    url = "https://github.com/kaa-ching/tbe";
+  src = fetchFromGitHub {
+    owner = "kaa-ching";
+    repo = pname;
     rev = "refs/tags/v${version}";
     sha256 = "1ag2cp346f9bz9qy6za6q54id44d2ypvkyhvnjha14qzzapwaysj";
   };