Update Echo options (#26)

Keeping bootstrap.js up-to-date with the latest pushes to `master` in the Laravel repo.

Author: austintoddj

src/bootstrap-stubs/bootstrap.js

@@ -51,5 +51,7 @@ if (token) {
 
 // window.Echo = new Echo({
 //     broadcaster: 'pusher',
-//     key: 'your-pusher-key'
+//     key: 'your-pusher-key',
+//     cluster: 'mt1',
+//     encrypted: true
 // });