fixed merging conflict

Author: trevordblack

src/TheNextWeek/bvh.h

@@ -18,6 +18,8 @@
 
 class bvh_node : public hittable  {
     public:
+        bvh_node();
+
         bvh_node(hittable_list& list, double time0, double time1)
             : bvh_node(list.objects, 0, list.objects.size(), time0, time1)
         {}