Add semicolon before conjunction "Or".

Author: shaunplee

books/RayTracingInOneWeekend.html

@@ -2810,7 +2810,7 @@
 
 You now have a cool ray tracer! What next?
 
-  1. Lights. You can do this explicitly, by sending shadow rays to lights. Or it can be done
+  1. Lights. You can do this explicitly, by sending shadow rays to lights; or it can be done
      implicitly by making some objects emit light, biasing scattered rays toward them, and then
      downweighting those rays to cancel out the bias. Both work. I am in the minority in favoring
      the latter approach.