HTTP status code should be passed as integer #9
Description
HTTP status code should be passed as integer to ResponseInterface::withStatus(), because string can lead to an error in some implementations (in [Slim](https://github.com/slimphp/Slim/blob/48fb2ce25255ad73f0c322f8914d289d8e55e923/Slim/Http
/Response.php#L206) for example).