Update hex requirement from 0.3 to 0.4

Updates the requirements on [hex](https://github.com/KokaKiwi/rust-hex) to permit the latest version.
- [Release notes](https://github.com/KokaKiwi/rust-hex/releases)
- [Commits](https://github.com/KokaKiwi/rust-hex/commits)

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

Cargo.toml

@@ -64,7 +64,7 @@ winapi = "0.3"
 
 [dev-dependencies]
 doc-comment = "0.3"
-hex = "0.3"
+hex = "0.4"
 itertools = "0.8"
 multiset = "0.0"
 regex = "1.0"