Hello,

Slack has released updates to its library and we can start using it for it. 

We especially like one change.

> slack_sdk has no required dependencies. This means aiohttp is no longer automatically resolved.

I've looked through the documentation and it doesn't look like a difficult task, but I think it's still worth testing.
More info: https://slack.dev/python-slack-sdk/v3-migration/index.html#from-slackclient-2-x

Best regards,
Kamil Breguła
tests/providers/slack/hooks/test_slack.py
def test_get_token_with_token_only(self):
        """tests `__get_token` method when only token is provided """
        
        test_token = 'test_token'
        test_conn_id = None
        
        hook = SlackHook(test_token, test_conn_id)
        
        output = hook.token
        expected = test_token
        assert output == expected
    @mock.patch('airflow.providers.slack.hooks.slack.WebClient')
    @mock.patch('airflow.providers.slack.hooks.slack.SlackHook.get_connection')
    def test_get_token_with_valid_slack_conn_id_only(self, get_connection_mock, mock_slack_client):
        """tests `__get_token` method when only connection is provided """
        
        test_token = None
        test_conn_id = 'x'
        test_password = 'test_password'
        
        get_connection_mock.return_value = mock.Mock(password=test_password)
        
        hook = SlackHook(test_token, test_conn_id)
        
        output = hook.token
        expected = test_password
        assert output == expected
        mock_slack_client.assert_called_once_with(test_password)
    @mock.patch('airflow.providers.slack.hooks.slack.SlackHook.get_connection')
    def test_get_token_with_no_password_slack_conn_id_only(self, get_connection_mock):