Use Ubuntu 14.04

Let's see if 14.04 works better. I don't feel like debugging the test
failure in a VM right now.  And I don't want to set up everything to
use Fedora (which is what my linux box is running).
Status Job ID Name Coverage
  Test
passed #363
linux
linux-runner

00:17:12

passed #364
osx
osx-runner

00:07:48