node-fetch version 3 breaks

[drshade]

Looks like there is a newer version of node-fetch (v3.0.0) which breaks when running Milkis (it looks like it's an ES module, which can't be require()'d the same way in foreign.js). I fixed my setup temporarily by rather doing a npm install --save node-fetch@2 to pick the older v2 version.

So either we should update README.md to pick version 2 of node-fetch, or update Milkis to support v3 of node-fetch. I'd be happy to take a crack at either and submit a PR if you like.

All the best, Tom