Don't use "with licenses;" for single licences

And don't use square brackets on such lines.

pkgs/applications/editors/vim/macvim.nix

@@ -87,7 +87,7 @@ stdenv.mkDerivation rec {
   meta = with stdenv.lib; {
     description = "Vim - the text editor - for Mac OS X";
     homepage    = https://github.com/b4winckler/macvim;
-    license = with licenses; [ vim ];
+    license = licenses.vim;
     maintainers = with maintainers; [ cstrahan ];
     platforms   = platforms.darwin;
   };