fixes bug 961142 - /crontabber_state/ reports stale numbers

@rhelmer r?

cc @lonnen @AdrianGaudebert

As of this change, the /crontabber_state/ reports very similarly except I've removed the `last_updated` key because it doesn't make any sense any more. 
And I've changed from the silly "2012-11-12 18:27:17.341895" format to "2012-11-12T18:27:17+00:00" which is the ISO format and contains the timezone information. 
The crontabber_state.js file that is used on https://crash-stats.mozilla.com/crontabber-state/ uses moment and it can parse both date formats equally.