Book 2 image updates: update image references

Author: hollasch

books/RayTracingTheNextWeek.html

@@ -396,7 +396,7 @@
 
 gives the following result:
 
-  ![Image 1: Bouncing spheres](../images/img-2.01-bouncing-spheres.jpg class=pixel)
+  ![Image 1: Bouncing spheres](../images/img-2.01-bouncing-spheres.png class=pixel)
 
 </div>
 
@@ -1264,7 +1264,7 @@
 
 We get:
 
-  ![Image 2: Spheres on checkered ground](../images/img-2.02-checker-ground.jpg class=pixel)
+  ![Image 2: Spheres on checkered ground](../images/img-2.02-checker-ground.png class=pixel)
 
 </div>
 
@@ -1349,7 +1349,7 @@
 <div class='together'>
 We get this result:
 
-  ![Image 3: Checkered spheres](../images/img-2.03-checker-spheres.jpg class=pixel)
+  ![Image 3: Checkered spheres](../images/img-2.03-checker-spheres.png class=pixel)
 
 </div>
 
@@ -1525,7 +1525,7 @@
 <div class='together'>
 Add the hashing does scramble as hoped:
 
-  ![Image 7: Hashed random texture](../images/img-2.07-hash-random.jpg class=pixel)
+  ![Image 7: Hashed random texture](../images/img-2.07-hash-random.png class=pixel)
 
 </div>