kiji-avro: SCHEMA-757. Update REVIEWERS file in kiji-avro.

issue: https://jira.kiji.org/browse/SCHEMA-757
review: https://review.kiji.org/r/1809
commit: https://github.com/kijiproject/kiji-avro/commit/70b5f70e3d57a8895d4c21fddf4b103823478034