Fixes CSS-display problems with HTTPS

Modern browsers denying to load the referenced resources (here CSS and JS)
with HTTP if the referring page was loaded HTTPS and complaining about "mixed
content".

This happens if you visit https://scala-lms.github.io/ as suggested by
some search engines.

Referring HTTPS resources from a HTTP page cause no problems. So
visiting http://scala-lms.github.io/ shouldn't cause any problems.