Update default.nix

pkgs/applications/graphics/gcolor2/default.nix

···
   meta = {
     description = "Simple GTK+2 color selector";
     homepage = http://gcolor2.sourceforge.net/;
+    license = stdenv.lib.licenses.gpl2Plus;
+    maintainers = with stdenv.lib.maintainers; [ notthemessiah ];
   };
 }