`--json` option doesn't output valid json

[jaygooby]

The json objects are single quoted and not double quoted, e.g.

[{'client_msg_id': '055bbe26-aa11-47cc-9ff7-effa09ef808b', 'type': 'message', 'text': 'blah blah', 'user': 'U01111'}]

so you can't then pipe this output to jq or other json parsing tools