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

And don't use square brackets on such lines.

pkgs/data/documentation/zeal/default.nix

@@ -30,7 +30,7 @@ stdenv.mkDerivation rec {
       app), available for Linux and Windows.
     '';
     homepage = "http://zealdocs.org/";
-    license = with stdenv.lib.licenses; [ gpl3 ];
+    license = stdenv.lib.licenses.gpl3;
     platforms = stdenv.lib.platforms.linux;
     maintainers = with stdenv.lib.maintainers; [ skeidel ];
   };