bug in "iter_from_json_file" method

[Surya291]

`

  if data_type == 'dict':
        data = json.load(json_file)
        for item in self.annotation_result_from_task(data):
            yield item

`

find this snippet at : label_studio_converter/converter.py , line : 360

json.load expects an fp , but according to arguments in this method json_file is a str (path of the file).

Please add a snippet to open the file as fp and use json.loads

Thanks!