code: function stop(opts, done) {
    debug('stopping...');
  
    killIfRunning(opts, function(err) {
      debug('Any running workers have been sent a stop command');
      done(err);
    });
  }
docs: Cleans up artifacts from this specific run and then kills the process.
  
  @param {Object} opts
  @param {Function} done
  @api private