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

And don't use square brackets on such lines.

pkgs/development/tools/alloy/default.nix

@@ -23,7 +23,7 @@ stdenv.mkDerivation rec {
     '';
     homepage = http://alloy.mit.edu/;
     downloadPage = http://alloy.mit.edu/alloy/download.html;
-    license = with licenses; mit;
+    license = licenses.mit;
     platforms = with platforms; linux;
     maintainers = with maintainers; [ nckx ];
   };