Fix time window checking.

That was a pain.

We now store the time (not just the date) when we notice the
number of people in space changing.

This lets us check better whether the user should get an update
or not. What with timezones and all that malarkey.
Specify ruby version
Merge branch 'master' into fix-timezone

Conflicts:
	Gemfile
Add debug output
Fix use of REDISTOGO_URL config setting
Try to fix use of REDISTOGO_URL
Tidy logging
Add logging for debugging
Fix test for recency of change
Remove debug logging