Upgrade to Scala 2.10.4.
Bump sbt version to 0.13.5-M3

We do not track snapshots of sbt because it seems like sbt-republish step
is not running on nightly basis anymore. Until this is solved, let's track
latest tagged build of sbt which is 0.13.5-M3 at the moment. This will
unbreak travis.

Also bump zinc version to 0.3.5-SNAPSHOT.
Merge pull request #51 from gkossakowski/upgrade-versions

Upgrade versions