Update nix requirement from 0.26 to 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@v0.26.0...v0.30.1)

---
updated-dependencies:
- dependency-name: nix
  dependency-version: 0.30.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

Cargo.toml

@@ -31,7 +31,7 @@ rand = "0.8"
 log = { version = "0.4", optional = true }
 
 [target.'cfg(unix)'.dependencies]
-nix = { version = "0.26", default-features = false, features = ["fs", "mman"] }
+nix = { version = "0.30", default-features = false, features = ["fs", "mman"] }
 libc = "0.2"
 
 [target.'cfg(windows)'.dependencies]