Bug on calculating bias

[farukbrgl]

When calculating bias for each key, in some combination there are zeros in hits. It causes bias=0.5. In the failing situations, obtained key bits always stuck at some values like f or ff

`bias = [ fabs(num_hits - float(NUM_P_C_PAIRS/2)) / float(NUM_P_C_PAIRS) for num_hits in hits ]`

Code line

You can add hits = [i for i in hits if i != 0] for removing zeros in hits.