DB schema generated by a migration may look different in
rails 4 and 5 (because rails 5 may use different default values).
For this reason it's important to explicitly set for which rails
version a migration was written for.

See https://stackoverflow.com/questions/35929869/activerecordmigration-deprecation-warning-asks-for-rails-version-but-im-no/35930912#35930912

This reverts commit 530f5158

.

See !4892.

Signed-off-by: Rémy Coutable <remy@rymai.me>

This reverts commit 9ca633eb, reversing
changes made to fb229bbf.

- Cherry-picked from `mvestergaard:branch-protection-dev-merge`
- https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4220