Bump service worker version

Author: domenic

resources.whatwg.org/standard-service-worker.js

@@ -8,7 +8,7 @@
 
 const standardShortname = location.host.split(".")[0];
 
-const cacheKey = "v12";
+const cacheKey = "v13";
 const toCache = [
   location.origin + "/",
   "https://resources.whatwg.org/spec.css",