Update fp_growth.py

I think sort should be the flowing, if use ori_way, when trans are :
       raw='25,48;25,48'
       or  raw ='25,52,48,274;71;71,274,33;52;25,52,48;274,71,33'
it has bugs
        ##def f2(v):
        ##    return items[v]+float(v)*0.1;
        ##transaction.sort(key=lambda v:f2(v),reverse=True)