Upgrade Node minimal version to 16
Mocha 10 and other dependencies (once updated) require node 14+ but we might as well take 16 and be OK for a while (16.15.0 being the current LTS).
Mocha 10 and other dependencies (once updated) require node 14+ but we might as well take 16 and be OK for a while (16.15.0 being the current LTS).