Update nix requirement from 0.24 to 0.26 (#179)

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@v0.24.0...v0.26.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

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

Author: dependabot[bot]

Cargo.toml

@@ -25,7 +25,7 @@ backtrace = { version = "0.3" }
 once_cell = "1.9"
 libc = "^0.2.66"
 log = "0.4"
-nix = { version = "0.24", default-features = false, features = ["signal", "fs"] }
+nix = { version = "0.26", default-features = false, features = ["signal", "fs"] }
 parking_lot = "0.12"
 tempfile = "3.1"
 thiserror = "1.0"