Service worker tweaks

[zplume]

Hi @hankchizljaw,

I've been testing out the service worker implementation in Hylia and noticed some opportunity for minor improvements, if you're interested:

• Serve an 'offline' page (from the pre-cache) if the user attempts to navigate while offline.
• Rebuild 11ty when src/_includes/partials/global/service-worker.js is updated.
• Exclude browser sync requests from the runtime cache (removes 'noise' from if you are testing on http://localhost / ngrok).

I've created a service-worker branch in my fork of Hylia with commits that address each of the above bullet points:
https://github.com/zplume/hylia/commits/service-worker

Would you be interested in a PR containing the above?

Thanks!

[Andy-set-studio]

Yes please, that would be great!