Triggered Events don't receive arguments

[cloudratha]

When triggering native SW events, they do not receive the event type.

https://github.com/zackargyle/service-workers/blob/526ee36ece5a761dfaa0464442f3ad6d9da56f8c/packages/service-worker-mock/utils/eventHandler.js#L7-L20

This is breaking pre-caching from Workbox, which specifically asserts the install event's type.

function createEvent(event, args) {
  switch (event) {
    case 'fetch':
      return new FetchEvent('fetch', getFetchArguments(args));
    case 'notificationclick':
      return new NotificationEvent(args);
    case 'push':
      return new PushEvent(args);
    case 'message':
      return new MessageEvent('message', args);
    default:
      return new ExtendableEvent(event, args);
  }
}

The above seems to produce the expected behaviour.

I attempted to fork and do a PR, however I cannot get the tests to pass on a clean install. Any advice?