Blog posts should always link to concrete versions of docs

[djencks]

There are many blog posts linking to "next" version, which is always wrong and will often cause broken links as the "next" docs evolve.

We should change all existing blog posts to link to concrete versions, or delink and note the version is no longer documented.

This might apply to the rest of the hugo-generated website, but I'm only aware of problems from the blog posts.