Note that the use of curl for the upgrade is on purpose: if the user had a old copy of github-keygen made with `git clone` and the remote is configured using SS

Note that the use of curl for the upgrade is on purpose: if the user had a old copy of github-keygen made with `git clone` and the remote is configured using SSH, a `git remote update && git rebase` would not work because of the revoked SSH key. So, in this case, I consider that curl over https is safer as long as your curl version is recent and your local repository of TLS certificiates is up to date.