Add missing listing highlight

Author: hollasch

books/RayTracingInOneWeekend.html

@@ -2113,9 +2113,12 @@
             ) const override {
                 auto scatter_direction = rec.normal + random_unit_vector();
 
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
                 // Catch degenerate scatter direction
                 if (scatter_direction.near_zero())
                     scatter_direction = rec.normal;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
 
                 scattered = ray(rec.p, scatter_direction);
                 attenuation = albedo;