Support RabbitMQ 3.9

[Askaholic]

Supposedly it's backwards compatible, but when I run the integration tests on the test server using the RabbitMQ 3.9 container I get the following error:

Traceback (most recent call last):
  File "/code/server/games/game.py", line 446, in on_game_end
    await self.process_game_results()
  File "/code/server/games/game.py", line 467, in process_game_results
    await self.game_service.publish_game_results(game_results)
  File "/code/server/game_service.py", line 228, in publish_game_results
    result_dict,
  File "/code/server/message_queue_service.py", line 154, in publish
    TRACE, "Published message %s to %s/%s", payload, exchange_name, routing
  File "/usr/local/lib/python3.7/site-packages/aio_pika/transaction.py", line 64, in __aexit__
    await self.commit()
  File "/usr/local/lib/python3.7/site-packages/aio_pika/transaction.py", line 50, in commit
    self.channel.tx_commit(), timeout=timeout,
  File "/usr/local/lib/python3.7/asyncio/tasks.py", line 414, in wait_for
    return await fut
  File "/usr/local/lib/python3.7/site-packages/aiormq/channel.py", line 764, in tx_commit
    return await self.rpc(spec.Tx.Commit(), timeout=timeout)
  File "/usr/local/lib/python3.7/site-packages/aiormq/base.py", line 168, in wrap
    return await self.create_task(func(self, *args, **kwargs))
  File "/usr/local/lib/python3.7/site-packages/aiormq/base.py", line 27, in __inner
    raise self.exception from e
  File "/usr/local/lib/python3.7/asyncio/tasks.py", line 630, in _wrap_awaitable
    return (yield from awaitable.__await__())
  File "/usr/local/lib/python3.7/site-packages/aiormq/base.py", line 27, in __inner
    raise self.exception from e
aiormq.exceptions.ChannelPreconditionFailed: PRECONDITION_FAILED - partial tx completion

When running RabbitMQ 3.8 no errors happen. There are also issues with running the unit tests when using 3.9. We'll have to figure out what the underlying issue is and what needs to change with our usage of aiopika to prevent these errors.

• Update unit tests to use 3.9
• Add RabbitMQ version to readme

[Brutus5000]

This error does not seem to occur on prod where RabbitMQ 3.9 is deployed for 2 weeks. The league service is receiving events and I do not see this error in the last hours of the logs.