Update rand requirement from 0.7.0 to 0.8.0 (#69)

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-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Cargo.toml

@@ -24,7 +24,7 @@ tokio-io = { version = "0.1.12", optional = true }
 futures = { version = "0.1.26", optional = true }
 
 [dev-dependencies]
-rand = "0.7.0"
+rand = "0.8.0"
 quickcheck = "0.9.0"
 tokio-core = "0.1.17"