Have a look at Netlify (https://www.netlify.com) - our free tier is like GitHub pages on steroids including HTTPS for custom domains (and deploy previews, use any build tool not just Jekyll, redirect rules, etc...).
According to the Netlify documentation[1], it looks like they support any/most tools, including Jekyll, Grunt, Middleman, Roots, Hugo, etc.
[0]: https://help.github.com/articles/using-jekyll-as-a-static-si...
Very nice service.