Add stacklevel argument to findCaller()

[domen13]

The following code

import logging
import logging_exceptions

logging.basicConfig()
logger = logging.getLogger('test')
logger.setLevel(logging.INFO)

logger.info('Test')

throws an error in Python 3.8

TypeError: findCaller() takes from 1 to 2 positional arguments but 3 were given

A new argument called stacklevel was added in findCaller() function in Python 3.8.