Update rand requirement from 0.7 to 0.8

Updates the requirements on [rand](https://github.com/rust-random/rand) to permit the latest version.
- [Release notes](https://github.com/rust-random/rand/releases)
- [Changelog](https://github.com/rust-random/rand/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-random/rand/compare/0.7.0...0.8.0)

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

Cargo.toml

@@ -30,7 +30,7 @@ log = { version = "0.4.11", features = ["std", "release_max_level_debug"] }
 socket2 = "0.3"
 parking_lot = "0.11"
 privdrop = "0.5.0"
-rand = "0.7"
+rand = "0.8"
 rustc-hash = "1"
 serde = "1.0"
 serde_derive = "1.0"