kiji-express-music: EXP-435. Update REVIEWERS file.

issue: https://jira.kiji.org/browse/EXP-435
review: https://review.kiji.org/r/1815
commit: https://github.com/kijiproject/kiji-express-music/commit/68b76aecdd24b31332d2f8524f208edd73daa83c