sendAttachment(recipientId, type, url, quickReplies, options) {
    const message = {
      attachment: {
        type,
        payload: { url }
      }
    };
    const formattedQuickReplies = this._formatQuickReplies(quickReplies);
    if (formattedQuickReplies && formattedQuickReplies.length > 0) {
      message.quick_replies = formattedQuickReplies;
    }
    return this.sendMessage(recipientId, message, options);
  }
@param {Recipient|String} recipientId
@param {String} type Must be 'image', 'audio', 'video' or 'file'.
@param {String} url URL of the attachment.
@param {Array.<QuickReply>} quickReplies
@param {SendMessageOptions} options