turn on sw for pwa

src/index.js

@@ -26,7 +26,7 @@ ReactDOM.render(
 // If you want your app to work offline and load faster, you can change
 // unregister() to register() below. Note this comes with some pitfalls.
 // Learn more about service workers: https://bit.ly/CRA-PWA
-serviceWorker.unregister();
+serviceWorker.register();
 // serviceWorker.register({
 //   onUpdate: registration => {
 //     const ready = window.confirm("New version available! Update?");