Is it “extravert” or “extrovert”?

This article about a recent study concerning the psychological benefits of introverts acting like extraverts is interesting, not just because it apparently conflates extraversion with “authenticity,” but also because of the comments that criticize the author for daring to use “extravert” instead of “extrovert.” Given some of the vehemence, you’d think you were reading a debate over the serial comma.