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* Fixes `56 <https://github.com/manheim/manheim-c7n-tools/issues/56>`__ - Bump c7n version from 0.9.4 to `0.9.10 <https://github.com/cloud-custodian/cloud-custodian/releases/tag/0.9.10.0>`__ and c7n-mailer from 0.6.3 to 0.6.9.
* Bump relax boto3 and botocore dependencies to work with c7n and new pip resolver.
* Add testing under Python 3.9; switch default Python version for tox/TravisCI to 3.9.
* Bump base Docker image to latest ``python:3.9.1-alpine3.12``
* Implement :ref:`policies.notify_only`.
* Fix failing test.