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.