kiji-music: EXP-420. Update to scala 2.10

issue: https://jira.kiji.org/browse/EXP-420
review: https://review.kiji.org/r/1702
commit: https://github.com/kijiproject/kiji-music/commit/e60e75a0a4df1a8f9ab4c830d09b1d0fabc8a8cb