Update rand requirement from 0.5 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/commits)

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

Author: dependabot-preview[bot]

Cargo.toml

@@ -25,5 +25,5 @@ maintenance = { status = "actively-developed" }
 twox-hash = "1.1"
 serde_derive = "1.0"
 serde = "1.0"
-rand = "0.5"
+rand = "0.7"
 packed_simd = { version = "0.3", features = ["into_bits"] }