kiji-schema: SCHEMA-764. Update REVIEWERS file.

issue: https://jira.kiji.org/browse/SCHEMA-764
review: https://review.kiji.org/r/1823
commit: https://github.com/kijiproject/kiji-schema/commit/b9d7cff1f8fa5257b7076fff7eb93e0f6e3a75db