Heartbeat issue

[davidworkman9]

If a user logs in and closes the browser before the heartbeat interval has elapsed they never get a heartbeat registered and thus never get logged out. I've fixed this for now by calling heartbeat in an onLogin callback, but I'm kind of thinking this is something the package should take care of. I was also wondering if it might be better to use debounce on the event handler rather than a setInterval.

I can do a pull request when I get some spare time, just wanted to put this out there for now in case anyone else runs into this.