Should we use npx?

[geoknee]

npx will fetch a package if you don't have it installed. I worry that using it will obscure any missing devDependencies.

I generally have my reservations about npx, but it seems that this change will unblock us in the short term. We can return to the issue of whether npx is the right choice, later.

Originally posted by @geoknee in #536 (comment)