Fix a build failure (#83)

modules/prediction/evaluator/vehicle/mlp_evaluator.cc

@@ -16,6 +16,7 @@
 
 #include <cmath>
 #include <fstream>
+#include <numeric>
 
 #include "modules/prediction/evaluator/vehicle/mlp_evaluator.h"
 #include "modules/prediction/common/prediction_gflags.h"
@@ -25,12 +26,6 @@
 namespace apollo {
 namespace prediction {
 
-MLPEvaluator::MLPEvaluator() {
-}
-
-MLPEvaluator::~MLPEvaluator() {
-}
-
 void MLPEvaluator::Clear() {
   obstacle_feature_values_map_.clear();
 }

modules/prediction/evaluator/vehicle/mlp_evaluator.h

@@ -32,9 +32,9 @@ namespace prediction {
 
 class MLPEvaluator : public Evaluator {
  public:
-  MLPEvaluator();
+  MLPEvaluator() = default;
 
-  virtual ~MLPEvaluator();
+  virtual ~MLPEvaluator() = default;
 
   void Evaluate(Obstacle* obstacle_ptr);