Finally I got jekyll work on github … as well as locally. Took me a day to understand little mistakes I did. 2 version of jekyll test by using

bundle list
bundle uninstall jekyll
# reinstall
bundle install jekyll

I add huge troubles with the _config.yml. It does not seems complex but I could not make it work. Right it is working both locally via

bundle exec jekyll serve

and on github. It is actually minimalist for the moment:

theme: minima
repository: "DGrv/dorian.gravier.github.io"
github: [metadata]