Fix renamed class.

Signed-off-by: Hugues Peccatte <hugues.peccatte@gmail.com>

server_plugins.php

@@ -5,6 +5,7 @@
  *
  * @package PhpMyAdmin
  */
+use PMA\libraries\Response;
 
 /**
  * requirements
@@ -14,7 +15,7 @@ require_once 'libraries/common.inc.php';
 /**
  * JS includes
  */
-$response = PMA_Response::getInstance();
+$response = Response::getInstance();
 $header   = $response->getHeader();
 $scripts  = $header->getScripts();
 $scripts->addFile('jquery/jquery.tablesorter.js');