Fix: Book2: Listing 70: Add missing bvh.h (#694)

Author: estshorter

CHANGELOG.md

@@ -12,6 +12,7 @@ Change Log -- Ray Tracing in One Weekend
 
 ### _The Next Week_
   - Delete: remove unused u,v,w variables in initial `perlin::noise()` function (#684)
+  - Fix: Listing 70: Add missing `bvh.h` (#694)
 
 
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books/RayTracingTheNextWeek.html

@@ -3246,6 +3246,10 @@
 why we get caustics and subsurface for free. It’s a double-edged design decision.
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+    ...
+    #include "bvh.h"
+    ...
+
     hittable_list final_scene() {
         hittable_list boxes1;
         auto ground = make_shared<lambertian>(color(0.48, 0.83, 0.53));