kiji-scoring-server: SCORSRVR-16. Updates scala maven plugin.

issue: https://jira.kiji.org/browse/SCORSRVR-16
review: https://review.kiji.org/r/1739
commit: https://github.com/kijiproject/kiji-scoring-server/commit/3b767d98459b44581a76ea7ed0ff73a219806937