Add support for Node Redis version 4.x clients

[soundslocke]

This would likely lead to a new 2.x release for this library which might not be backwards compatible with Node Redis clients of version 3.x. It would depend on whether there is a clean way to differentiate between client instance types. Something to look into.

I'm also not sure how useful this would be given Node Redis 4.x supports scan iterators now. One use might be in providing methods which return all of the gathered values at once, which would be less verbose/cumbersome than writing iterator loops every time you want to scan and could be preferable, given the context. 🤔