@slack/client v4.2.0

• Allows mrkdwn_in and callback_id fields in message attachments for formatting on attachment fields (#528) - thanks @DominikPalo
• Fixes optionality of validate argument for channels.join method (#530) - thanks @DominikPalo
• Adds the users.conversations method (#532) - thanks @DominikPalo
• Fixes overwriting of default parameters after send() call (#535) - thanks @franckbrignoli
• Fixes and adds logging for unexpected websocket close in StateMachine (#537) - thanks @shanedewael