Chore: drop Node.js 8 support

Following up with https://github.com/netlify/cli/issues/1568, we should be good now with dropping Node.js 8 support for the zip-it-and-ship-it.

[eduardoboucas]

This sounds great, thanks for following up on this @ehmicky!

I’ve assigned this to myself, I’m happy to take it from here.

[ehmicky]

After doing some research, I would suggest that we directly drop Node 8 support in the whole package (including list() and listAll()) due to the very minimal risk:

• No npm package seems to require @netlify/functions-utils directly
• The only plugin using @netlify/functions-utils is netlify-plugin-inline-functions-env. From Humio logs, it appears that no site using this plugin is both installing it in package.json and using Node 8
• The risk of local plugins using utils.functions while using Node 8 seems minimal, although there is no available data about this

What are your thoughts?

Note: this would also moving the require('archiver') statement back to the top-level scope.