fix the average label for binary classification.
fix the average label for binary classification.

henry0312/LightGBM,henry0312/LightGBM,olofer/LightGBM,olofer/LightGBM,Laurae2/LightGBM,microsoft/LightGBM,wxchan/LightGBM,microsoft/LightGBM,microsoft/LightGBM,olofer/LightGBM,olofer/LightGBM,huanzhang12/lightgbm-gpu,wxchan/LightGBM,henry0312/LightGBM,Allardvm/LightGBM,huanzhang12/lightgbm-gpu,fstonezst/LightGBM,wxchan/LightGBM,henry0312/LightGBM,fstonezst/LightGBM,huanzhang12/LightGBM,wxchan/LightGBM,microsoft/LightGBM,Allardvm/LightGBM,fstonezst/LightGBM,henry0312/LightGBM,huanzhang12/lightgbm-gpu,huanzhang12/LightGBM,Laurae2/LightGBM,Laurae2/LightGBM,huanzhang12/LightGBM,Laurae2/LightGBM,fstonezst/LightGBM,Allardvm/LightGBM,huanzhang12/lightgbm-gpu,huanzhang12/LightGBM,Laurae2/LightGBM,fstonezst/LightGBM,Allardvm/LightGBM,microsoft/LightGBM,wxchan/LightGBM,olofer/LightGBM,huanzhang12/LightGBM,Allardvm/LightGBM,huanzhang12/lightgbm-gpu