Made PR change requests, including spurious colon and small english touch up

Author: trevordblack

books/RayTracingTheNextWeek.html

@@ -1683,7 +1683,7 @@
 </div>
 
 <div class='together'>
-We then add that scale to the `two_perlin_spheres()` scene description::
+We then add that scale to the `two_perlin_spheres()` scene description:
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     hittable_list two_perlin_spheres() {
@@ -2084,8 +2084,8 @@
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     [Listing [rtw-stb-image]: <kbd>[rtw_stb_image.h]</kbd> Include the stb_image package]
 
-The above assumes that you have copied the `stb_image.h` into a folder called `export`. Adjust as
-per your directory structure.
+The above assumes that you have copied the `stb_image.h` into a folder called `external`. Adjust
+according to your directory structure.
 </div>