ExtendedJsonFormatter issue on format

[vltr]

https://github.com/async-worker/aiologger/blob/ed53c805fdcd653445a624561a71a01ba4cf6cc6/aiologger/formatters/json.py#L175

howdy! shouldn't this be msg[self.default_msg_fieldname] = record.msg, just like the JsonFormatter ? there's probably something else to be done on line 173 if msg is already present in the dict (IMO).

cheers!