Update renderer.php

Co-authored-by: Maximilian Haye <[email protected]>

Author: MartinGauk

renderer.php

@@ -266,6 +266,7 @@ protected function add_package_js_calls(array $jscalls, array $roles, question_d
     protected function get_iframe_js_before(): string {
         return <<<'END'
 <script>
+    "use strict";
     (function () {
         // Add <base target='_blank'> tag to head so links are opened in a new tab.
         const base = document.createElement('base');