Update env_logger requirement from 0.7.1 to 0.8.3 (#1992)

Updates the requirements on [env_logger](https://github.com/env-logger-rs/env_logger) to permit the latest version.
- [Release notes](https://github.com/env-logger-rs/env_logger/releases)
- [Changelog](https://github.com/env-logger-rs/env_logger/blob/master/CHANGELOG.md)
- [Commits](https://github.com/env-logger-rs/env_logger/commits/v0.8.3)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Max Inden <mail@max-inden.de>

protocols/relay/Cargo.toml

@@ -29,7 +29,7 @@ wasm-timer = "0.2"
 prost-build = "0.7"
 
 [dev-dependencies]
-env_logger = "0.7.1"
+env_logger = "0.8.3"
 libp2p = { path = "../.." }
 libp2p-kad = { path = "../kad" }
 libp2p-ping = { path = "../ping" }