kiji-bento: Revert "EXP-420. Update to scala 2.10" for Dashi 1.4.3 release.

This reverts commit 55bcba05910a9d632593f2e833f2003ea318d59c.
commit: https://github.com/kijiproject/kiji-bento/commit/87982d136e7e33c57f99b3fdf51279f6229d97e3