Remove duplicated ParentModel in test file
Override activerecord destroy!

As of https://github.com/rails/rails/commit/5aab0c053832ded70a3a4b58cb97f8f8bba796ba
that is the method called when destroying associated records.

Example: Both Article and Comment models acts_as_paranoid. Once an
article is destroyed it's expected that all of its comments are
destroyed the same way by only touching the deleted_at column rather
than permanently removing the object from the database.
Run travis build on both rails 4.0 and 4.1