Thank you for the test.
I have different output.
I have checked line 120 in footer.php
Ok. I have found the problem. We are using different templates. The template which I use misses this section in the main.tpl file in style folder. So I have added it here and it works now.
And I'm using this command:
$forum_loader->add_js('https://code.jquery.com/jquery-1.11.3.js',array('group' => FORUM_JS_GROUP_SYSTEM));