Fix URL reference to Service worker

Extra '/' made the service worker to be searched from the root

Author: diekus

swreg.js

@@ -1,5 +1,5 @@
 if ('serviceWorker' in navigator) {
-  navigator.serviceWorker.register('/sw.js').then(function(registration) {
+  navigator.serviceWorker.register('sw.js').then(function(registration) {
     // Registration was successful
     console.log('ServiceWorker registration successful with scope: ', registration.scope);
   }).catch(function(err) {