kiji-schema-shell: DDLSHELL-68. Update REVIEWERS file.

issue: https://jira.kiji.org/browse/DDLSHELL-68
review: https://review.kiji.org/r/1825
commit: https://github.com/kijiproject/kiji-schema-shell/commit/5f9a96b5636ab18286a0fa67a79c92f34edb01c2