Build issue with ruby 3.0

[pthouvenin]

Issue

Building with the most recent version of ruby (3.0) currently fails with the following error, since github-pages does not currently support the latest version of ruby (see github-pages issue).

Solution

Staying with the 2.7 version of ruby is a possible solution, see github/pages-gem#752.

It might be a good idea to mention this point in the README.

[guilgautier]

Thanks for catching this issue @pthouvenin !