Fix for compatibility with PayPlans 3.x

ARS doesn't work correctly with PayPlans 3.x. This fix solves the problem.

More in detail, the call to 'PayplansApi::getUser($user_id)->getSubscriptions($status)' gives an array of objects with the subscriptions details for the user while 'PayplansApi::getUser($user_id)->getPlans($status)' returns an array of plans ids.