message: docs: fix JsonPrintOptions link
diff: @@ -64,7 +64,7 @@ services
  print_options
  *(optional, object)* Control options for response json. These options are passed directly to
  `JsonPrintOptions <https://developers.google.com/protocol-buffers/docs/reference/cpp/
  - google.protobuf.util.json_util#JsonPrintOptions>`. Valid options are:
  + google.protobuf.util.json_util#JsonPrintOptions>`_. Valid options are:
  add_whitespace
  *(optional, boolean)* Whether to add spaces, line breaks and indentation to make the JSON
  