Merge pull request #474 from zgxmy/dev-minor

Fix an image-url error in book2

Author: hollasch

books/RayTracingTheNextWeek.html

@@ -2245,7 +2245,7 @@
 
   <div class="render">
 
-  ![Empty Cornell box](../images/img.cornell-empty.jpg)
+  ![Empty Cornell box](../images/img.cornell-first.jpg)
 
   </div>