fix BehaviorParametersEditor for m_UseChildSensors (#3404)

com.unity.ml-agents/Editor/BehaviorParametersEditor.cs

             EditorGUI.indentLevel--;
             EditorGUILayout.PropertyField(so.FindProperty("m_BehaviorType"));
             EditorGUILayout.PropertyField(so.FindProperty("m_TeamID"));
-            EditorGUILayout.PropertyField(so.FindProperty("m_useChildSensors"), true);
+            EditorGUILayout.PropertyField(so.FindProperty("m_UseChildSensors"), true);
             // EditorGUILayout.PropertyField(serializedObject.FindProperty("m_Heuristic"), true);
             EditorGUI.indentLevel--;
             if (EditorGUI.EndChangeCheck())