Fix failing test for RepoSubscription.for

- Removed assertiion with the result of RepoSubscription.for.
- It was returning of ActiveRecord::Relation result which was being
- compared with array
- This method is getting tested from eariler assertion
    `assert_equal [sub1], user.repo_subscriptions_for(repo.id)`
Merge pull request #198 from prathamesh-sonpatki/fix-tests

Fix failing test for RepoSubscription.for