Disable/hide email button for authors 

who haven't published in the previous six months.

Applies to https://github.com/GigaOM/gigaom/issues/4939
An alternative to what's suggested in https://github.com/GigaOM/go-author-bio-widget/pull/4#discussion_r15879662 would be to call the wrapper method `_last_post_date()` (note the underscore) and only return a post date, uncached. The underscore prefix is used commonly throughout WP to indicate private callbacks of a similarly named method.