message: fix a little bug in paddle_serving_server __init__.py by HexToString
diff: @@ -754,6 +754,7 @@ class MultiLangServerServiceServicer(multi_lang_general_model_service_pb2_grpc.
  ret = self.bclient_.predict(
  feed=feed_batch,
  fetch=fetch_names,
  + batch=True,
  need_variant_tag=True,
  log_id=log_id)
  return self._pack_inference_response(ret, fetch_names, is_python)
  