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.
There is a PR for that already.  Was hoping you guys would merge it. 

-Evan
"Never doubt that a small group of thoughtful, committed citizens can change the world" - M. Mead

> On Aug 6, 2014, at 5:27 AM, Marc Slemko <notifications@github.com> wrote:
> 
> In project/build.sbt:
> 
> > @@ -3,11 +3,11 @@ resolvers ++= Seq(
> >      "DiversIT repo" at "http://repository-diversit.forge.cloudbees.com/release"
> >  )
> >  
> > -addSbtPlugin("com.socrata" % "socrata-cloudbees-sbt" % "1.2.3")
> > +addSbtPlugin("com.socrata" % "socrata-cloudbees-sbt" % "1.2.4-SNAPSHOT")
> We need to build socrata-cloudbees-sbt against 0.13.
> 
> —
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