Update rand requirement from 0.5.5 to 0.6.1

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/0.6.1)

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

Cargo.toml

@@ -53,7 +53,7 @@ features = ["common", "serde"]
 cgmath =  { version = "0.16" }
 criterion = "0.2"
 ron = "0.4"
-rand = "0.5.5"
+rand = "0.6.1"
 serde_json = "1.0"
 specs-derive = { path = "specs-derive", version = "0.3.0" }