code: function() {
        let undelivered = this.published.reset();
        if (undelivered.length > 0) {
          return Promise.map(undelivered, (message) => {
            return this.channel.publish(message);
          });
        }
        return Promise.resolve(true);
      }
docs: Republish any undelivered messages (called upon connection)
  
  @public
  @memberOf ExchangeMachine.prototype
  @returns {Promise} a promise that is fulfilled when publication is complete