Add an uptime endpoint for Pingdom.

Sends a simple database query to see if we can still connect
to the database. Should help us detect issues like yesterday's
EC2 issues earlier.
Add tests for /uptime.
Bump travis-core.

Includes updated payload for repositories.
Merge pull request #72 from travis-ci/mm-uptime-endpoint

Add an uptime endpoint for Pingdom
Merge branch 'mm-update-core'