chore(cargo): update env_logger requirement from 0.8.4 to 0.9.0 (#6)

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/main/CHANGELOG.md)
- [Commits](https://github.com/env-logger-rs/env_logger/compare/v0.8.4...v0.9.0)

---
updated-dependencies:
- dependency-name: env_logger
  dependency-type: direct:production
...

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Cargo.toml

@@ -19,5 +19,5 @@ chrono = "0.4"
 serde_json = "1.0"
 typetag = "0.1"
 log = "0.4.0"
-env_logger = "0.8.4"
+env_logger = "0.9.0"
 serde = { version = "1.0", features = ["derive"] }