Update Changelog entry for strong zones.
Update Changelog entry for strong zones.

Change-Id: I15dac60dfec77315dd3701c066c546fe979f3f0a
Reviewed-on: https://dart-review.googlesource.com/7400
Reviewed-by: Kevin Moore <1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@google.com>

dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk