The site is currently not compatible with Jekyll >=3.5.0. So I have added a Gemfile to help with installation of the correct version.
bundle install
jekyll build
jekyll serve
If you encounter the following error when building/serving the site:
Liquid Exception: undefined method `scan' for #<Liquid::VariableLookup:0x0055555872ca10> in sitemap.xml
Then you likely have multiple versions of jekyll installed. Either uninstall the jekyll versions >=3.5.0 with sudo gem uninstall jekyll or specify the desired version at run-time.
jekyll _3.4.5_ build
jekyll _3.4.5_ serve