refs https://github.com/TryGhost/Toolbox/issues/174
- right now, our migrations manually check the client of the knex
instance to see whether we're running on MySQL or SQLite
- that's been working fine, but the problem is that we're due to switch
to the mysql2 driver soon, so all these checks will be faulty
- i've altered the functionality of `@tryghost/database-info` to accept
a knex instance, and it'll return if the DB is MySQL or SQLite in some
helper functions
- this commit bumps the package and switches to that format
- originally I used a shared instance of the class within
`@tryghost/database-info` but there's a chance that the knex instance
inside migrations actually comes from knex-migrator, and not Ghost, so
that wouldn't work
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.
