Reduce the external files required for gem installation

assets/js/pwa/app.js

@@ -0,0 +1,9 @@
+---
+layout: compress
+permalink: '/app.js'
+---
+
+/* Registering Service Worker */
+if('serviceWorker' in navigator) {
+  navigator.serviceWorker.register('{{ "/sw.js" | relative_url }}');
+};