Require Node.js 12

[sindresorhus]

Node.js 10 is soon out of LTS (in April), so I think it makes sense to do it for this major release.

This PR also prepares us for ESM. The ESM move is blocked by: avajs/typescript#5 (comment)

[sindresorhus]

@szmarczak I tried to remove

got/source/core/index.ts

Lines 1391 to 1392 in 2369580

	// TODO: Remove this when targeting Node.js >= 12
	this._progressCallbacks = [];

and it's relevant code, but tests started failing. How do you intend to remove it?

[szmarczak]

it's relevant code, but tests started failing. How do you intend to remove it?

Let me see...

[szmarczak]

pem crashes on macOS

[szmarczak]

I'm not really sure why but this line fails on Node.js 12 only: https://github.com/nodejs/node/blob/v12.20.1/lib/_http_client.js#L472 only when running timeout tests. If a timeout gets breached then Node.js throws that assertion error.

[sindresorhus]

pem crashes on macOS

That's an issue in master too.

I'm not really sure why but this line fails on Node.js 12 only: https://github.com/nodejs/node/blob/v12.20.1/lib/_http_client.js#L472 only when running timeout tests. If a timeout gets breached then Node.js throws that assertion error.

This is also an existing issue in master. Should definitely be fixed, but not really relevant to this PR.