In the page footer under "Development", the links for GPL and OTW are http links. They should be updated to https links.
The relevant line is:
<a href="http://www.gnu.org/licenses/gpl-2.0.html" title="View License">GPL</a> by the <a href="http://transformativeworks.org/" title="The Organization for Transformative Works">OTW</a>
The links should be updated to https://www.gnu.org/licenses/gpl-2.0.html and https://transformativeworks.org/