Update rand requirement from 0.4 to 0.7

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/rand_core-0.4.0...0.7.3)

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

Cargo.toml

@@ -22,7 +22,7 @@ thiserror = "1.0"
 
 [dev-dependencies]
 bencher = "0.1"
-rand = "0.4"
+rand = "0.7"
 walkdir = "1.0"
 
 [features]