Update node versions

[bajtos]

• Add support for Node.js 13.x
• Drop support for Node 8.x

Checklist

👉 Read and sign the CLA (Contributor License Agreement) 👈

• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• Commit messages are following our guidelines

[jannyHou]

👍 LGTM (please rebase before merge)

[bajtos]

We will release this change as semver-minor. Cross-posting from loopbackio/loopback-connector#172 (comment):

Ideally, when we remove support for a major Node.js version (e.g. 8.x), then we should publish a major version of our module too.

Unfortunately, this does not work well with our LTS support policy. If we keep supporting EOL versions of Node, and there is a security vulnerability discovered in one of our dependencies, and this vulnerability is fixed in the latest version only, and that latest version no longer supports EOLed version of Node, then we cannot get the fix. If we are not able to fix security vulnerabilities in our LTS versions, then it's IMO no long-term support at all.

We have discussed this for a bit around Node.js 4.x release (pretty much the first relevant release after 2-3 years of having everybody on Node.js 0.10). I believe we reached the conclusion that when having to choose between security fixes and strict adherence to semver rules, we prefer security over user convenience.

BTW this gets even more complicated for major versions of the framework itself (e.g. loopback and loopback-datasource-juggler module). When LB 3.x is Current and LB 2.x is Active LTS, and Node.js 6.x goes EOL, then how should be drop support for Node.js 6.x from LB 2.x? LB 3.x is already taken at that point...

My recommendation is to use package-lock and npm-shrinkwrap functionality to lock down dependencies in your project to the latest versions that still supports the end-of-life Node.js version you are using (e.g. 8.x).