Considering that the official Syslinux git repo is located at:
repo.or.cz/syslinux.git
and just in case the following information might be relevant to
Syslinux's devs/others...
Quote from repo.or.cz:
***
repo.or.cz will soon switch to Let's Encrypt for its TLS certificates.
This means that we will no longer issue the site's certificates
ourselves. If you have configured your browser or your Git client to
only trust the existing CA (see root certificate), access to the site
will stop working. Please configure your clients to trust the Let's
Encrypt CA instead, after we have switched the certificates. This will
not have any effect on SSH access.
We plan to discontinue support of the old certificate at the start of
October 2018.
***
Regards,
Ady.