fix the average label for binary classification.

src/boosting/gbdt.cpp

@@ -301,10 +301,14 @@ bool GBDT::TrainOneIter(const score_t* gradient, const score_t* hessian, bool is
       for (data_size_t i = 0; i < num_data_; ++i) {
         sum_per_class[static_cast<int>(label[i])] += 1.0f;
       }
-    } else {
+    } else if(sigmoid_ < 0.0f){
       for (data_size_t i = 0; i < num_data_; ++i) {
         sum_per_class[0] += label[i];
       }
+    } else {
+      for (data_size_t i = 0; i < num_data_; ++i) {
+        sum_per_class[0] += label[i] > 0;
+      }
     }
     std::vector<double > init_scores(num_class_);
     for (int i = 0; i < num_class_; ++i) {