disable monotone constraint in objective functions with renew_tree_output (#3380)
disable monotone constraint in objective functions with renew_tree_output (#3380)

* Update gbdt.cpp

* Update gbdt.cpp

* Apply suggestions from code review
henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,microsoft/LightGBM,henry0312/LightGBM