startPolling(options = {}) {
    if (this.hasOpenWebHook()) {
      return Promise.reject(new errors.FatalError('Polling and WebHook are mutually exclusive'));
    }
    options.restart = typeof options.restart === 'undefined' ? true : options.restart;
    if (!this._polling) {
      this._polling = new TelegramBotPolling(this);
    }
    return this._polling.start(options);
  }
Start polling.
Rejects returned promise if a WebHook is being used by this instance.
@param {Object} [options]
@param {Boolean} [options.restart=true] Consecutive calls to this method causes polling to be restarted
@return {Promise}