fixes bug 1072373 - Upgrade to crontabber 0.13

@twobraids r?

I tested it locally and ran my sample app with it too. 
Seems a certain "lars" needs to look over his editor and how it cleans up trailing spaces :)
https://github.com/mozilla/socorro/commit/ecb90adc26ae6a098f4ca11d8e10a694a6ecc373