Fix attribute serialization (Webklex#179)

Author: netpok

src/Attribute.php

@@ -61,22 +61,13 @@ public function toString(){
         return $this->__toString();
     }
 
-    /**
-     * Return the serialized attribute
-     *
-     * @return array
-     */
-    public function __serialize(){
-        return $this->values;
-    }
-
     /**
      * Convert instance to array
      *
      * @return array
      */
     public function toArray(){
-        return $this->__serialize();
+        return $this->values;
     }
 
     /**