Support for 0 low frequency cutoff

Currently, a zero low frequency cutoff is not supported. Is there a reason why?
https://github.com/vail-systems/node-mfcc/blob/master/src/mfcc.js#L46

Note that zero is the default value in a Python MFCC module
https://github.com/jameslyons/python_speech_features/blob/master/python_speech_features/base.py#L64