Update Workbox to 4.1.0

Created by: jadbox

Currently the generated service worker workbox version is: importScripts("https://storage.googleapis.com/workbox-cdn/releases/3.6.3/workbox-sw.js")

The latest is 4.1: see https://github.com/GoogleChrome/workbox/releases The import can now read as: importScripts("https://storage.googleapis.com/workbox-cdn/releases/4.1.0/workbox-sw.js")

This update improves a number of things, including adding the much needed skipWaiting() message handler: https://github.com/GoogleChrome/workbox/pull/1929