kiji-modeling: MODELING-25. Fix the default value of numReducers on Recommendation Pipe.

issue: https://jira.kiji.org/browse/MODELING-25
review: https://review.kiji.org/r/1598
commit: https://github.com/kijiproject/kiji-modeling/commit/6130c6c0291511df3baff176e6631251f6b7e1d0