Certificate issue with phenopackets.org

It seems the certificate that's being served when you access https://phenopackets.org/ is for `*.github.io` as opposed to `phenopackets.org`, which causes most browsers to throw an error.

There's a "Custom Domain" option in the repo settings, at Settings -> Pages; setting it to `phenopackets.org` should resolve this issue. You can read more about GitHub Pages custom domains here: https://docs.github.com/en/pages/configuring-a-custom-domain-for-your-github-pages-site

Open the repository's Settings -> Pages configuration and verify the custom domain is set to phenopackets.org. Confirm the site loads over HTTPS without a certificate warning and serves a certificate covering phenopackets.org.

Written by the indexing model from the issue text.