chore(deps): update env_logger requirement from 0.7 to 0.8

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](rust-cli/env_logger@v0.7.0...v0.8.1)

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

examples/Cargo.toml

@@ -30,7 +30,7 @@ futures = "0.3"
 tokio = { version = "0.2.12", features = ["full"] }
 
 # env-logger example
-env_logger = "0.7"
+env_logger = "0.8"
 
 # tower examples
 tower = "0.3"

tracing-log/Cargo.toml

@@ -26,7 +26,7 @@ trace-logger = []
 tracing-core = { path = "../tracing-core", version = "0.2"}
 log = { version = "0.4" }
 lazy_static = "1.3.0"
-env_logger = { version = "0.7", optional = true }
+env_logger = { version = "0.8", optional = true }
 
 [dev-dependencies]
 tracing = { path = "../tracing", version = "0.2"}