Always generate datestamp for deploys from UTC

My local computer is on EST, and our server is on UTC. This caused a fun bug, where I had done 5 server-generated deploys (using the webhook) that used UTC time, and then ran a manual one from my computer (5 hours behind).

This meant that the old deploy cleanup task, which keeps the 5 most recent deploys, was actually deleting the newest deploy, because its EST timestamp was *older* than the previous UT timestamp timezones I'd deployed. This caused the server to go down, because it shifted the `current/` symlink to a directory that had just been deleted during trhe cleanup.

This PR ensures that the timezone used to generate deployed datestamps will always be consistent.