code: function(res) {
        console.log('SUBSCRIBE');
        var MSG_SUBSCRIBE = this.conf.CONST.MSG_SUBSCRIBE;
        if (_.isArray(MSG_SUBSCRIBE)) {
          res.reply(_.sample(MSG_SUBSCRIBE));
        } else {
          res.reply(MSG_SUBSCRIBE);
        }
        return;
      }
docs: /*
  Called when a user subscribes. Respond plain text
  conf.CONST.MSG_SUBSCRIBE to client by default.
  
  Now rolling message is supported. conf.CONST.MSG_SUBSCRIBE could be an
  array, _subscribe() will choose one of them randomly. Even an object
  which represents a reply-with-pic is allowed to be in the array.
  
  *res*, will call res.reply() to respond to client.