Microdata for “publisher” should be a structured value, not a “Thing”

[aperezdc]

I have just noticed that even when the “new” (current) validator says in its results that all is fine, the “old” one's results complain that the “publisher” entity should not be a “Thing”... I suppose that if the newer one is okay with the metadata, we can merge this as-is for now; because right now I don't have the bandwidth to figure out how to write down structured microdata using a <meta> tag.

Originally posted by @aperezdc in #77 (comment)