kiji-bento: BENTO-99. `source kiji-env.sh` causes error on OS X

issue: https://jira.kiji.org/browse/BENTO-99
review: https://review.kiji.org/r/2118
commit: https://github.com/kijiproject/kiji-bento/commit/1b55a2ef8d22358fa6ed1a79b9420f653603c246