also consider "author" taxonomy query when testing whether we should add author opengraph metadata

I think we need @misterbisson's eyes on this one.

see https://github.com/GigaOM/gigaom/issues/4904
I don't think this is the fix we're looking for. I can see it will work around the problem, but think the issue is in coauthors plus or our go-local plugin for not triggering the is_author() condition. That's likely going to cause other bugs if we leave it as-is.