Wrap replace with unicode function call in neg_token

[rwl]

In order to get controllers to work with Python 2.7 I had to wrap the replace operation with a unicode call in the neg_token function. I suspect this is a Python 2 only issue and has no effect when using Python 3.

            if unicode(x.replace('.','0')).isnumeric() == True:

PYPOWER-Dynamics/pydyn/controller.py

Line 197 in bb90844

if x.replace('.','0').isnumeric() == True: