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](rust-random/rand@0.7.0...0.8.0)

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

Cargo.toml

@@ -45,7 +45,7 @@ serde = { version = "1", optional = true, default-features = false }
 [dev-dependencies]
 # TODO This will probably be part of rust in the future (see https://github.com/rust-lang/rust/issues/29553)
 criterion = "0.3"
-rand = "0.7"
+rand = "0.8"
 # needed to test serde
 bincode = "1"
 pretty_assertions = "0.6"