Update nix to 0.20

[printfn]

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[Detegr]

Is there a specific reason why nix should be updated to the latest version?

[ghost]

To throw my 2 cents in, one of nix dependencies is cfg-if. Specifically nix v0.18 depends on cfg-if v0.1.

In one of my projects I also depend on rand which in turn depends on cfg-if v1.0. nix v0.19 upgrades its cfg-if version to 1.0 as well.

Having separate versions in the dependency tree causes issues with, for example, generating documentation as both versions of cfg-if are named the same, but technically are different crates bc of the different versions, so cargo doc throws up a warning about it. So upgrading the version would resolve that clash.

This is a known issue within cargo and its tracking issue can be found here.

My case is a rather knit-picky case and I can continue working just fine without the update, but to update the dependency would be a quality of life improvement in my workflow.

[Nukesor]

First of all, thanks for providing this library :)

I second @Fluhzar's statement. nix 0.20 already got released and ctrlc is one of the main sources of duplicate dependencies in my projects. (duplicate nix version + duplicate cfg-if version).

It would be awesome if this PR could be updated to 0.20 and merged afterwards!

Stuff like this significantly reduces compile-time and at least I consider keeping dependencies up-to-date a best practice.

Thanks again for your time and effort maintaining this library!

Cheers

[Detegr]

Thanks for the comments and sorry for taking so long :)