Update PhpDebugBarMiddleware.php

Author: prolic

src/PhpDebugBarMiddleware.php

@@ -9,6 +9,7 @@
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Message\UriInterface;
 use Psr\Http\Server\MiddlewareInterface;
+use Psr\Http\Server\RequestHandlerInterface;
 use Slim\Http\Uri;
 use Zend\Diactoros\Response;
 use Zend\Diactoros\Response\HtmlResponse;