Rewrite ppm example in chapter 2 InOneWeekend to match actual output. Resolves #321

Author: trevordblack

books/RayTracingInOneWeekend.html

@@ -140,18 +140,10 @@
     1 253 51
     2 253 51
     3 253 51
-    4 253 51
     5 253 51
     6 253 51
     7 253 51
     8 253 51
-    9 253 51
-    10 253 51
-    11 253 51
-    12 253 51
-    13 253 51
-    14 253 51
-    15 253 51
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     [Listing [first-img]: First image output]
 </div>