Correctly handle metadata in JSON templates

The dict will be copied as is rather than transformed into a list.

Closes yskoht#93

keymapviz/__init__.py

@@ -107,7 +107,7 @@ def __legends(self, keymap):
     def __json_format(self, json_, keymap):
         legends = self.__legends(keymap)
         ret = [[_.format(*legends) if isinstance(_, str) else _ for _ in __]
-               for __ in json_]
+               if isinstance(__, list) else __ for __ in json_]
         with io.StringIO() as sio:
             json.dump(ret, sio, indent=4)
             ret_str = sio.getvalue()