Update env_logger requirement from 0.5 to 0.6

Updates the requirements on [env_logger](https://github.com/sebasmagri/env_logger) to permit the latest version.
- [Release notes](https://github.com/sebasmagri/env_logger/releases)
- [Commits](https://github.com/sebasmagri/env_logger/commits/v0.6.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot-support

unwind/Cargo.toml

@@ -14,7 +14,7 @@ gcc = "0.3.52"
 
 [dev-dependencies]
 backtrace = "0.3"
-env_logger = "0.5"
+env_logger = "0.6"
 
 [features]
 nightly = []