Fix cancellations from webhook

* BUG FIX: Fixed an issue where cancelled subscriptions would remove the members membership prematurely. It now will only remove the membership once CCBill sends through the "Expiration" webhook which is the end of term.

webhook.php

@@ -45,7 +45,7 @@
 
 	break;
 
-	case 'Cancellation':
+	case 'Expiration':
 
 		$subscription_id = sanitize_text_field( $response['subscriptionId'] );