kiji-mapreduce: KIJIMR-272. Update REVIEWERS file.

issue: https://jira.kiji.org/browse/KIJIMR-272
review: https://review.kiji.org/r/1817
commit: https://github.com/kijiproject/kiji-mapreduce/commit/dbf50655fc628afb3673a4799bf0fd7e916159b2