Update env_logger requirement from 0.7.1 to 0.8.1

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/compare/v0.7.1...v0.8.1)

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

Cargo.toml

@@ -35,5 +35,5 @@ optional = true
 version = "0.2.3"
 
 [dev-dependencies]
-env_logger = "0.7.1"
+env_logger = "0.8.1"
 net2 = "0.2.33"