lock production gems
lock production gems

PG has deprecated certain constants and only rails 5.x is aware of it.
This lock will prevent updating PG to version that will break the app.

Slim-rails latest patch is breaking the tests. Locking it to v3.1.1 for
now.

ministryofjustice/fr-staffapp,ministryofjustice/fr-staffapp,ministryofjustice/fr-staffapp,ministryofjustice/fr-staffapp