Mark this update as complete.

        We index the parameters `update_id` and `date`.

def touch(self):
        """
        Mark this update as complete.

        We index the parameters `update_id` and `date`.
        """
        marker_key = self.marker_key()
        self.redis_client.hset(marker_key, 'update_id', self.update_id)
        self.redis_client.hset(marker_key, 'date', datetime.datetime.now())

        if self.expire is not None:
            self.redis_client.expire(marker_key, self.expire)