Fix es6 warning

Author: raujonas

extension.js

@@ -6,7 +6,8 @@ const Gio = imports.gi.Gio;
 const ExtensionUtils = imports.misc.extensionUtils;
 const Me = ExtensionUtils.getCurrentExtension();
 
-let output, box, settings, gschema, stopped;
+let output, box, gschema, stopped;
+var settings;
 
 function init() { 
     //nothing todo here