Describe the bug

The https://twitter.github.io/scala_school/ page contains some links to deprecated subdomains of GH Pages in github.com. This causes a 404 error when an user try to click in one of these links.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://twitter.github.io/scala_school/
2. Click on "Effective Scala" in "Also" section
3. See error

Expected behavior

We expect that the link described above has as target the page: https://twitter.github.io/effectivescala/

Screenshots
If applicable, add screenshots to help explain your problem.

Environment

Any browser

Additional context

https://github.blog/changelog/2021-01-29-github-pages-will-stop-redirecting-pages-sites-from-github-com-after-april-15-2021/