Cumulative flag should be tested against False

[jrbenito]

canadianSolar-pvoutput/canadian_reads.py

Line 251 in 11b87cf

power_imp=None, temp=None, vdc=None, cumulative=False, vac=None,

canadianSolar-pvoutput/canadian_reads.py

Line 278 in 11b87cf

if cumulative is not None:

Cumulative flag is being defined as False by default and tested against None, this causes C1=1 for every single request.

Better to test it against True instead of redefine it as None because this way any non default value besides True will end up default c1 at pvoutput (default as today is c1=0)