service-worker: await unnecessary, errors should be handled

[sidewayss]

Pretty simple stuff, minimal code changed. await as the last command in a function is pointless. Errors thrown during the completion of a promise should be handled. Low probability of errors in this project as-is, but high probability of errors for any newbie adapting this example for their own project.

The two calls to caches.match() could use similar .catch() blocks, but I left them alone for now. They're easy enough to add before merging if you all decide to include them.

[skyclouds2001]

The original function is intended to throw the exception to the outside where the function is called, whether its thrown exception should be handled or not completely decided by outside caller.
The fix make it outside caller unable to handle it any more.

Another issue is that the original function will end only when the put execution ends, but the fix make the outside caller unable to detect when function ends.

So I believe the fix is not correct and should be closed.