Bump version to SBT 0.13.5-RC2

> On Sat, May 10, 2014 at 1:06 PM, Grzegorz Kossakowski <grek@typesafe.com> wrote:
> I reproduced the problem. It's due to the fact that we are using
> sbt 0.13.2-M1 in dbuild which doesn't include a bug fix for the
> issue we ran into.
>
> Upgrading to sbt 0.13.5-RC2 restores dbuild stability.