Fixed update method for Products repository
Fixed update method for Products repository

no-issue

When updating a Product we can pass existing Stripe Prices, these will
either be adding to the database, or updated if they already exist. When
updating them we were attemping to use the `id` passed in the update,
which is not necessarily included. Instead we should use the `id` of the
StripePrice which we have already retrieved from the database.

TryGhost/Ghost,TryGhost/Ghost,TryGhost/Ghost