Docs: Update github-pages gem for Jekyll 3.9 and Kramdown 2
Docs: Update github-pages gem for Jekyll 3.9 and Kramdown 2

Addresses https://github.com/advisories/GHSA-mqm2-cgpr-p4m6.

Ref https://github.com/jekyll/jekyll/issues/8315.
Ref https://jekyllrb.com/news/2020/08/05/jekyll-3-9-0-released/.

qunitjs/qunit,qunitjs/qunit