kiji-express: EXP-336.  Fix mistake in KijiOutput Scaladoc.

review: https://review.kiji.org/r/1484
issue: https://jira.kiji.org/EXP-336
commit: https://github.com/kijiproject/kiji-express/commit/6233741d2f1ba7527ae9f1ee8dca0cd64a1fa1bd