Fix build url

Services/Webservice.php

@@ -196,7 +196,7 @@ class Webservice
         }
 
         if ($order_by) {
-            $url .= http_build_query(array('order_by' => $order_by));
+            $url .= '&' . http_build_query(array('order_by' => $order_by));
         }
 
         if ($limit) {