Gravity Forms Stripe Addon 5.6.0

- Updated callback error 'entry_not_found' to return a header status of 404.
- Updated Stripe API library to version 5.9.2.
- Fixed security issue.
- Fixed security issue.
- Fixed subscriptions not being processed when using Stripe API version 2018-02-05 or newer.

- Fixed subscriptions not being processed when using Stripe API version 2018-02-05 or newer.
- Updated Stripe API library to version 5.9.2.

- Added GPL to plugin header.
- Added the "gform_stripe_subscription_params_pre_update_customer" filter allowing the subscription parameters to be overridden before the customer is subscribed to the plan.
- Added support for webhook signing secrets.
- Updated Plugin URI and Author URI to use https.
- Updated webhook processing to use the API mode specified in the received event.
- Updated Stripe API library to version 5.1.3.
- Fixed API mode used to retrieve webhook event when signing secret is configured.
- Fixed the card type validation message containing "false" in some situations.