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

And don't use square brackets on such lines.

pkgs/development/libraries/libkeyfinder/default.nix

@@ -14,7 +14,7 @@ stdenv.mkDerivation rec {
   meta = with stdenv.lib; {
     description = "Musical key detection for digital audio (C++ library)";
     homepage = http://www.ibrahimshaath.co.uk/keyfinder/;
-    license = with licenses; gpl3Plus;
+    license = licenses.gpl3Plus;
     platforms = with platforms; linux;
     maintainers = with maintainers; [ nckx ];
   };