fix(pwa) fix loading the service worker

We typically use a base URL for static assets using a CDN so loading the worker
from there won't work since it's a different origin. Using a URL relative to the
origin of the page will make it be loaded from the right place.

index.html

@@ -25,7 +25,7 @@
 
             if (shouldRegisterWorker) {
                 navigator.serviceWorker
-                    .register('pwa-worker.js')
+                    .register('/pwa-worker.js')
                     .then(reg => {
                         console.log('Service worker registered.', reg);
                     })
@@ -33,7 +33,7 @@
                         console.log(err);
                     });
             }
-        })
+        });
     </script>
     <script>
         // IE11 and earlier can be identified via their user agent and be