[css-fonts] Broken reference link

[Ms2ger]

https://drafts.csswg.org/css-fonts-3/#src-desc

The [RFC8081] reference links to #ref-RFC8081 rather than #ref-rfc8081 as it should.

CC @tabatkins

[svgeesus]

Thanks!

This is caused by Fonts 3 using the old, obsolete preprocessor written by Bert; the references database for it is out of date and does not have RFC 8081, so I have to add it in by hand after Overview.src.html is converted to Overview.html.

I will be sure to edit it in correctly next time.