Update nix requirement from 0.27.1 to 0.28.0 (#776)

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@v0.27.1...v0.28.0)

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

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

crates/livesplit-hotkey/Cargo.toml

@@ -25,7 +25,7 @@ mio = { version = "0.8.0", default-features = false, features = [
     "os-ext",
     "os-poll",
 ], optional = true }
-nix = { version = "0.27.1", features = ["user"], optional = true }
+nix = { version = "0.28.0", features = ["user"], optional = true }
 promising-future = { version = "0.2.4", optional = true }
 x11-dl = { version = "2.20.0", optional = true }