USE A CDN (CLOUDFLARE)
By the far, the more efficient way to increase your score is to use a free content delivery network to serve your site. I recommend the free version of CloudFlare because of its simplicity. There are a few reasons for this:
The CDN will automatically minify your HTML, CSS and JavaScript.
Google PageSpeed requires this.
GitHub Pages by default places a caching header of 10 minutes on all
resources. Google will throw a “Leverage browser caching” error for
this. You can override this from the CDN. On CloudFlare, I did this
by creating a Page Rule (in addition to the general caching option)
that sets the Cache level on everything to a minimum of 8 days
(Google’s recommendation). I am not using the Rocket Loader option.
The CDN will automatically Gzip elements, such as SVG’s (even though
they’re served from GitHub)
Setting up the CDN will by far increase your PageSpeed results, but
it may take up to 24 hours for your CDN setting changes to propagate
(you won’t see them reflected in Google’s results immediately.)