update public interface for getUserFolder

lib/public/iservercontainer.php

@@ -81,9 +81,10 @@ interface IServerContainer {
 	/**
 	 * Returns a view to ownCloud's files folder
 	 *
+	 * @param string $userId user ID
 	 * @return \OCP\Files\Folder
 	 */
-	function getUserFolder();
+	function getUserFolder($userId = null);
 
 	/**
 	 * Returns an app-specific view in ownClouds data directory