Update spec_helper to use engine_cart properly

The old dummy application was still hanging around is spec_helper. Also,
this pins a `factory_girl` to 4.4.0. The recent 4.5.0 update to breaks
the linter for ActiveTriples by assuming there is a database involved in
the models. I'll submit an issue to the `factory_girl` folks.
Merge pull request #5 from dpla/fix-spec-helper

Update spec_helper to use engine_cart properly