Reschedule nightlies for middle of the night

[brson]

Somehow I have never noticed that nightly builds are running at 6 PM Pacific time because the build master is on UTC. These should be happening at 2 AM. Remember to update the cron job that does cloudfront invalidation.

[brson]

I think I'm not going to bother touching this after all. @alexcrichton points out that the complete builds take 5 hours anyway, finishing in the middle of the night.