kiji-model-repository: KIJIREPO-52.  Fix backwards assert in PMML tool.

review: https://review.kiji.org/r/1758
issue: https://jira.kiji.org/KIJIREPO-52
commit: https://github.com/kijiproject/kiji-model-repository/commit/0c04ed64dce598c94edf3b272c552326a2a97a27