message: Fix comment linting errors.
  Stop listening and cleanup endpoints correctly.
diff: @@ -227,8 +227,8 @@ export default React.createClass({
  },
  componentWillUnmount() {
  - WidgetMessaging.stopListening();
  - WidgetMessaging.removeEndpoint(this.props.id, this.props.url);
  + this.widgetMessaging.stopListening();
  + this.widgetMessaging.removeEndpoint(this.props.id, this.props.url);
  window.removeEventListener('message', this._onMessage);
  },
  