Update Rollup to use HMR with Sapper

src/service-worker.js

@@ -7,6 +7,7 @@ const ASSETS = `cache${timestamp}`
 const to_cache = shell.concat(files)
 const cached = new Set(to_cache)
 
+// Install
 self.addEventListener('install', event => {
 	event.waitUntil(
 		caches
@@ -18,6 +19,7 @@ self.addEventListener('install', event => {
 	)
 })
 
+// Activate
 self.addEventListener('activate', event => {
 	event.waitUntil(
 		caches.keys().then(async keys => {
@@ -31,6 +33,7 @@ self.addEventListener('activate', event => {
 	)
 })
 
+// Fetch
 self.addEventListener('fetch', event => {
 	if (event.request.method !== 'GET' || event.request.headers.has('range')) return