Original title: Decide when to drop support for Python 3.6

context_vars can solve this but they were introduced in Python 3.7: https://www.python.org/dev/peps/pep-0567/

Python 3.6 support ends in a few days time, and it looks like Glitch has updated to 3.7 now - so maybe I can get away with Datasette needing 3.7 these days?

Tweeted about that here: https://twitter.com/simonw/status/1473761478155010048

Originally posted by @simonw in #1576 (comment)