build(deps): bump nix from 0.19.1 to 0.20.0

Bumps [nix](https://github.com/nix-rust/nix) from 0.19.1 to 0.20.0.
- [Release notes](https://github.com/nix-rust/nix/releases)
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](https://github.com/nix-rust/nix/commits)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Cargo.toml

@@ -84,7 +84,7 @@ winapi = { version = "0.3.9", features = [
 ] }
 
 [target.'cfg(not(windows))'.dependencies]
-nix = "0.19.1"
+nix = "0.20.0"
 
 [build-dependencies]
 shadow-rs = "0.5.24"