Downgrade to sbt 0.13.2-M1

The sbt 0.13.2 has some Ivy-related regression that makes dbuild fail.
The sbt 0.13.2-M1 appears to work fine and includes name hashing so we
can support projects that switched to name hashing incremental compilation
mode.
Merge pull request #34 from gkossakowski/sbt-0.13.2-M1

Downgrade to sbt 0.13.2-M1