0.12.4: Fix scala version, 0.12.4 uses v2.9.2.

See: https://github.com/sbt/sbt/blob/0.12.4/project/Sbt.scala#L19
Merge pull request #820 from dwijnand/patch-1

0.12.4: Fix scala version, 0.12.4 uses v2.9.2.