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
'security-10-6'
[10.6] Prevent notes on confidential issues from being sent to chat
See merge request gitlab/gitlabhq!2366
# Conflicts:
# app/helpers/services_helper.rb