Fixed Double JSON Encoding

- Updated PPModel to not double encode urls in Json String.

lib/PayPal/Common/PPModel.php

@@ -218,7 +218,10 @@ class PPModel
      */
     public function toJSON($options = 0)
     {
-        return json_encode($this->toArray(), $options);
+        // Because of PHP Version 5.3, we cannot use JSON_UNESCAPED_SLASHES option
+        // Instead we would use the str_replace command for now.
+        // TODO: Replace this code with return json_encode($this->toArray(), $options | 64); once we support PHP >= 5.4
+        return str_replace('\\/', '/', json_encode($this->toArray(), $options));
     }
 
     /**