Update nix requirement from 0.27.0 to 0.28.0 (#30)

Updates the requirements on [nix](https://github.com/nix-rust/nix) to permit the latest version.
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](nix-rust/nix@v0.27.0...v0.28.0)

---
updated-dependencies:
- dependency-name: nix
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Cargo.toml

@@ -10,7 +10,7 @@ keywords = ["command", "process", "child", "subprocess", "fd"]
 categories = ["os::unix-apis"]
 
 [dependencies]
-nix = { version = "0.27.0", features = ["fs"] }
+nix = { version = "0.28.0", features = ["fs"] }
 thiserror = "1.0.24"
 tokio-crate = { package = "tokio", version = "1.32.0", optional = true, default-features = false, features = [
   "process",