Drop support for Node.js 12 or use a transpiler

[0x2b3bfa0]

Node.js 12 is in maintenance mode and will stop being supported on 2022-04-30. It would be nice to start using, Node.js 14 or even 16 to take advantage of features like optional chaining as per #581 (comment).

[DavidGOrtega]

I don't have to wait for a specific node version we can always use a transpiler :)

[0x2b3bfa0]

If we choose that path, it would be nice to consider TypeScript. Anyhow, we can remain in the pure JavaScript realms with Babel or something similar.

[0x2b3bfa0]

See also iterative/setup-cml#40

[0x2b3bfa0]

Already using optional chaining:

• Add support for Bitbucket native uploads  #943 (review)