Please petition Github to support HTTPS on github pages: https://github.com/contact
Here's what I wrote:
Obviously, a lot of people want HTTPS for github pages:
Until recently, that would be difficult to implement but, as it turns out, the implementation is pretty much complete:
I'm a freelancer, so I've got time and I'd love to help out in any way I can (I'd even come work for you at a substandard rate) if we could get this implemented by Let's Encrypt launch day.
You can also send a message to email@example.com