bugfix: prevent badge from blinking

To test it:

1. login on http://alpha.happy-dev.fr/, so you can add unread notifications from the admin if needed.
2. in the repository, go in examples/notifications.html, replace bind-user (l.36) by a data-src with the uri of your user account on alpha. For example, for me it is: https://api.alpha.happy-dev.fr/users/matthieu/
3. at the root of sib-notifications, launch a server (python3 -m http.server 8001)

The page should be accessible at: http://localhost:8001/examples/notifications.html

Now, every 30 second, the counter should refresh without blinking.