Logging will be broken by dart-lang/logging#71

[jamesderlin]

I've recently made a change (dart-lang/logging#71) that affects the behavior of Logger.detached from package:logging. This change expected to be included in logging 0.11.4.

This change in behavior should not affect most packages, but it appears that it will break logging in the s3_cache_image package.

The recommended fix is to set Logger.level and Logger.onRecord on the detached Logger itself instead of on Logger.root. (In general, libraries should leave responsibility for configuring Logger.root to the application.)