MFH: r441673

Switch to USE_GITHUB.

fedorahosted.org is down and the project has switched to GitHub.

Comparing the GitHub tarball and the old one from distcache.FreeBSD.org, the
former has a few new files:

• .gitignore
• extras/img/omping-banner-url.svg
• extras/img/omping-banner.svg
• extras/img/omping-icon.svg

All the other contents are identical.

PR: 218099

Approved by: ports-secteam (blanket approval)