issue with encoding in python3

[TC-matthew-wenger]

I'm getting an encoding error in python3 when taking the app out of debug mode and running warner.py

Traceback (most recent call last):
  File "/Users/matthew.wenger/destalinator/warner.py", line 18, in <module>
    Warner().warn(force_warn=force_warn)
  File "/Users/matthew.wenger/destalinator/warner.py", line 11, in warn
    self.ds.warn_all(self.config.warn_threshold, force_warn)
  File "/Users/matthew.wenger/destalinator/destalinator.py", line 229, in warn_all
    if self.warn(channel, days, force_warn):
  File "/Users/matthew.wenger/destalinator/destalinator.py", line 214, in warn
    self.post_marked_up_message(channel_name, self.warning_text, message_type='channel_warning')
  File "/Users/matthew.wenger/destalinator/destalinator.py", line 108, in post_marked_up_message
    self.slacker.post_message(channel_name, self.add_slack_channel_markup(message), **kwargs)
  File "/Users/matthew.wenger/destalinator/slacker.py", line 325, in post_message
    post_data['attachments'] = json.dumps([{'fallback': message_type}], encoding='utf-8')
  File "/usr/local/Cellar/[email protected]/3.9.6/Frameworks/Python.framework/Versions/3.9/lib/python3.9/json/__init__.py", line 234, in dumps
    return cls(
TypeError: __init__() got an unexpected keyword argument 'encoding'

[christofdamian]

this might be a duplicate of #161 and could be fixed as a part of #211