build(deps): update nix requirement from 0.17.0 to 0.18.0

Updates the requirements on [nix](https://github.com/nix-rust/nix) to permit the latest version.
- [Release notes](https://github.com/nix-rust/nix/releases)
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](nix-rust/nix@v0.17.0...v0.18.0)

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

heim-common/Cargo.toml

@@ -20,7 +20,7 @@ uom = { version = "0.28.0", default-features = false, features = ["autoconvert",
 backtrace = { version = "~0.3", optional = true }
 
 [target.'cfg(unix)'.dependencies]
-nix = "0.17.0"
+nix = "0.18.0"
 lazy_static = "1.3.0"
 
 [target.'cfg(target_os = "windows")'.dependencies]

heim-net/Cargo.toml

@@ -19,7 +19,7 @@ macaddr = "1.0"
 libc = "~0.2"
 
 [target.'cfg(unix)'.dependencies]
-nix = "0.17.0"
+nix = "0.18.0"
 
 [dev-dependencies]
 heim-derive = { version = "0.1.0-beta.1", path = "../heim-derive" }