closes https://github.com/TryGhost/Team/issues/557
After updating to v4 on SQLite from v3, we were unable to delete members due to a foreign key mismatch error. This is because the migrations which recreates the tables for `members_stripe_customers_subscriptions` and `members_stripe_customers` doesn't add back the unique constraint which is needed by FKs for reference.
The migration creates the missing UNIQUE constraints on the tables.