Bump nix from 0.28.0 to 0.29.0

Bumps [nix](https://github.com/nix-rust/nix) from 0.28.0 to 0.29.0.
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](nix-rust/nix@v0.28.0...v0.29.0)

---
updated-dependencies:
- dependency-name: nix
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Cargo.toml

@@ -19,7 +19,7 @@ slog = "^2.7"
 slog-async = "^2.8"
 slog-term = "^2.9"
 crossbeam-channel = "^0.5"
-nix = { version = "^0.28", features = ["socket", "user"]}
+nix = { version = "^0.29", features = ["socket", "user"]}
 num-derive = "^0.3"
 num-traits = "^0.2"
 sd-notify = "^0.4"