I’m a little late writing a post on this, but this blog (and a few other sites I have on GitHub) is now being served over HTTPS.
GitHub enabled the feature for custom domains on May 1st. Making the switch is usually as easy as ticking a checkbox:
One of my domains doesn’t seem compatible at the moment, however:
Not sure if it’s because of the age of the repo or what, but I didn’t have any issues with my other repos.