Gravity Forms Stripe Addon 5.6.0

- Fixed processing of "invoice.payment_succeeded" and "invoice.payment_failed" events with Stripe API version 2018-05-21.

- Added support for the "charge.expired" event; changing the entry payment status from Authorized to Voided when an authorization expires.
- Fixed a refund transaction being recorded in the sales tab when an authorized charge is manually released via the Stripe.com dashboard.

- Reverted the callback error 'entry_not_found' to return a header status code of 200.
- Added the "gform_stripe_entry_not_found_status_code" filter enabling the status code to be overridden.