Improvement request: disable when there's no network connection

[micalevisk]

Pretty much as is doing here: https://github.com/sindresorhus/notifier-for-github/blob/f1facf697f07bc01a030da358c953e4df0155127/source/background.js#L120

Instead of always running the update function, I think it would be nice to check if navigator.onLine

firefox-github-notifier/background.js

Lines 5 to 6 in aef4672

	async function update() {
	let options,

just add the following on above if (!navigator.onLine) return; I guess.