Remove protocol to resolve to https automatically from the browser

[heryxpc]

TL;DR the styles won't load if serving via HTTPS when loading URL from site.github.url

We are using this template at https://github.com/JConfMexico/jalapenio/blob/cbc700b1d3fe285a761510c5fae7036aafaa22bf/_config.yml#L15

Noticed that the CSS styles break after we enable HTTPS to Github Pages. This is a common mixed content error documented by Github.

This appears to be a common issue on Github pages when using the scriptlet default: site.github.url. Applied the general pattern discussed there to allow the browser to self-resolve the protocol.