setStickerMaskPosition(sticker, form = {}) {
    form.sticker = sticker;
    if (form.mask_position) {
      form.mask_position = stringify(form.mask_position);
    }
    return this._request('setStickerMaskPosition', { form });
  }
Use this method to change the [mask position](https://core.telegram.org/bots/api#maskposition) of a mask sticker.

The sticker must belong to a sticker set created by the bot.

@param {String} sticker File identifier of the sticker
@param {Object} [options] Additional Telegram query options
@return {Promise} True on success
@see https://core.telegram.org/bots/api#setstickermaskposition