def message_on_success_dag(**context):
    """Hangouts Chat incoming webhook quickstart."""
    dag_id = context.get('task_instance').dag_id
    end_date = datetime.utcnow().strftime("%Y-%m-%d %H:%m")

    bot_message = {
        'text': "DAG *{dag}*, marking as Success, "
                "scheduled at {date_time}".format(dag=dag_id, date_time=end_date)
    }

    message_headers = {'Content-Type': 'application/json; charset=UTF-8'}
    http_obj = Http()

    return http_obj.request(
        uri=webhook_url,
        method='POST',
        headers=message_headers,
        body=dumps(bot_message)
    )

Traceback (most recent call last)
  File "/usr/local/lib/airflow/airflow/models/__init__.py", line 1495, in _run_raw_tas
    self.xcom_push(key=XCOM_RETURN_KEY, value=result
  File "/usr/local/lib/airflow/airflow/models/__init__.py", line 1919, in xcom_pus
    execution_date=execution_date or self.execution_date
  File "/usr/local/lib/airflow/airflow/utils/db.py", line 73, in wrappe
    return func(*args, **kwargs
  File "/usr/local/lib/airflow/airflow/models/__init__.py", line 4595, in se
    value = json.dumps(value).encode('UTF-8'
  File "/opt/python3.6/lib/python3.6/json/__init__.py", line 231, in dump
    return _default_encoder.encode(obj
  File "/opt/python3.6/lib/python3.6/json/encoder.py", line 199, in encod
    chunks = self.iterencode(o, _one_shot=True
  File "/opt/python3.6/lib/python3.6/json/encoder.py", line 257, in iterencod
    return _iterencode(o, 0
  File "/opt/python3.6/lib/python3.6/json/encoder.py", line 180, in defaul
    o.__class__.__name__