Cache headers are set to expire after 10 minutes at GitHub pages.
Which is a bit too restrictive on js, images or css files.
It would be nice if these cache headers could be set to a larger period (1 year, or something similar). I'm not certain if any engineering hurdles or dangers exist in doing so, and I'm not implying this is something that can easily be done - since obviously GitHub didn't do it for their Pages.
Good job!