log littering

Created by: voidpp

https://github.com/doctormo/python-crontab/blob/master/crontab.py#L153 If I import the crontab module, the basicConfig add a new definitely unwanted handler to the logging and duplicate every log messages for me (with a shitty format, but it's irrelevant).

python-crontab version: 2.3.0+