Set cost type to integer

This seems to be a remnant of when the code dealt with crypt() directly. The password_hash() function expects the cost option to be an LVAL (it does a type conversion for strings).

src/Symfony/Component/Security/Core/Encoder/BCryptPasswordEncoder.php

@@ -42,7 +42,7 @@ public function __construct($cost)
             throw new \InvalidArgumentException('Cost must be in the range of 4-31.');
         }
 
-        $this->cost = sprintf('%02d', $cost);
+        $this->cost = $cost;
     }
 
     /**