Log Message:
py-kombu: updated to 4.2.1

4.2.1:
The 4.2.0 release contained remains of the async module by accident.
This is now fixed.
- Handle librabbitmq fileno raising a ValueError when socket is not connected.

4.2.0:
- Now passing max_retries, interval_start, interval_step,
  interval_max parameters from broker transport_options to
  :meth:~kombu.Connection.ensure_connection when returning
  :meth:~kombu.Connection.default_connection
- Qpid: messages are now durable by default
- Kombu now requires version 2.10.4 or greater of the redis library,
  in line with Celery
- Fixed ImportError in some environments with outdated simplejson
- MongoDB: fixed failure on MongoDB versions with an "-rc" tag
- Ensure periodic polling frequency does not exceed timeout in
  virtual transport
- Fixed string handling when using python-future module
- Replaced "async" with "asynchronous" in preparation for \ 
Python 3.7
- Allow removing pool size limit when in use