Update listing 2.38 caption

Author: hollasch

books/RayTracingTheNextWeek.html

@@ -2222,7 +2222,7 @@
             auto k = int(floor(p.z()));
             ...
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-    [Listing [perlin-smoothed]: <kbd>[perlin.h]</kbd> Perlin smoothed]
+    [Listing [perlin-smoothed]: <kbd>[perlin.h]</kbd> Perlin with Hermitian smoothing]
 
 <div class='together'>
 This gives a smoother looking image: