Copy one of the old directories into a new one.
Then:
cd new-presentation/
make Gemfile
bundle
From this exact directory.
Prepare npm for Reveal.js:
pushd reveal.js
npm install
npm install -g grunt
npm install -g decktape
popd
Regenerate the CSS:
cp revealjs-css/ribose.scss reveal.js/css/theme/source/
pushd reveal.js
grunt css-themes
popd
cp reveal.js/css/theme/ribose.css revealjs-css/