stop(options = {}) {
    if (!this._lastRequest) {
      return Promise.resolve();
    }
    const lastRequest = this._lastRequest;
    this._lastRequest = null;
    clearTimeout(this._pollingTimeout);
    if (options.cancel) {
      const reason = options.reason || 'Polling stop';
      lastRequest.cancel(reason);
      return Promise.resolve();
    }
    this._abort = true;
    return lastRequest.finally(() => {
      this._abort = false;
    });
  }
Stop polling
@param  {Object} [options] Options
@param  {Boolean} [options.cancel] Cancel current request
@param  {String} [options.reason] Reason for stopping polling
@return {Promise}