code: function (err) {
  		if (this.jobs.length) {
  			var job = this.jobs.shift();
  			try {
  				job(err, this);
  			} catch (e) {
  				this.next(e);
  			}
  		} else {
  			this.running = false;
  		}
  	}
docs: Run the next job in queue
  
  @private
  @param  {Object} err