updated serviceworker

serviceWorker.js

@@ -26,12 +26,8 @@ self.addEventListener('install', function(event){
 
 self.addEventListener('fetch', function(event){
     event.respondWith(
-        caches.open(APP_SHELL_CACHE).then(function(cache) {
-            return fetch(event.request)
-                .then(function(response){
-                    cache.put(event.request, response.clone());
-                    return response;
-                });
+        caches.match(event.request).then(function(response) {
+            return response || fetch(event.request);
         })
     );
 });