Fix: Listing 40: Change perlin.h in the caption to texture.h (#698)

Author: estshorter

CHANGELOG.md

@@ -14,6 +14,7 @@ Change Log -- Ray Tracing in One Weekend
   - Delete: remove unused u,v,w variables in initial `perlin::noise()` function (#684)
   - Fix: Listing 15: In `bvh.h`, add missing `hittable_list.h` include (#690)
   - Fix: Listing 33, 34, 38: Change implicit casts to explicit ones (#692)
+  - Fix: Listing 40: Change `perlin.h` in the caption to `texture.h` (#698)
 
 
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books/RayTracingTheNextWeek.html

@@ -1864,7 +1864,7 @@
             double scale;
     };
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-    [Listing [perlin-smoothed-2]: <kbd>[perlin.h]</kbd> Perlin smoothed, higher frequency]
+    [Listing [perlin-smoothed-2]: <kbd>[texture.h]</kbd> Perlin smoothed, higher frequency]
 </div>
 
 <div class='together'>