Some of the walls -> some of the walls

Author: trevordblack

books/RayTracingTheNextWeek.html

@@ -1908,7 +1908,7 @@
 </div>
 
 <div class='together'>
-This is very noisy because the light is small. But we have a problem: Some of the walls are facing
+This is very noisy because the light is small. But we have a problem: some of the walls are facing
 the wrong way. We haven't specified that a diffuse material should behave differently on different
 faces of the object, but what if the Cornell box had a different pattern on the inside and outside
 walls? The rectangle objects are described such that their front face is always in the $(1, 0, 0)$,