Upgrade to SBT 0.13 and enable code coverage

Title says it all.    You can try it by running `scoverage:test` command in SBT.

After the newer version of socrata-cloudbees-sbt plugin is released, then the version in `project/build.sbt` needs to be updated.
Ahh, ok, I see it.  1.2.4 got built without it and I must have missed the notification on that, so I was confused.  Will take a look.