Update tokio requirement from 0.2 to 0.3

Updates the requirements on [tokio](https://github.com/tokio-rs/tokio) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](tokio-rs/tokio@tokio-0.2.0...tokio-0.3.5)

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

Cargo.toml

@@ -5,7 +5,7 @@ authors = ["Luna <git@nyx.nova.fail>"]
 edition = "2018"
 
 [dependencies]
-tokio = { version = "0.2", features = ["macros"] }
+tokio = { version = "0.3", features = ["macros"] }
 rand = "0.7"
 meval = "0.2"
 lazy_static = "1.4"