Huh, they're using Github pages. I thought if you set up a redirect - a C dns response - to whatever.github.io, that would soothe the ssl complaints in the browser.

Looking at the dns records, it looks like they didn't do this, and instead set up an A record.

I realized Github probably documents this, and found: https://help.github.com/articles/using-a-custom-domain-with-...

My suggestion would likely work for a www subdomain, but not for the apex domain.