Fix boolean

Author: AntoineLemaire

src/Message/CancelSubscriptionRequest.php

@@ -40,11 +40,11 @@ public function getData()
         $this->validate('subscriptionReference');
 
         if ($this->parameters->has('invoice_now')) {
-            $data['invoice_now'] = (bool)$this->getParameter('invoice_now');
+            $data['invoice_now'] = $this->getParameter('invoice_now') ? 'true' : 'false';
         }
 
         if ($this->parameters->has('prorate')) {
-            $data['prorate'] = (bool)$this->getParameter('prorate');
+            $data['prorate'] = $this->getParameter('prorate') ? 'true' : 'false';
         }
 
         return array();