Fixed another small grammatical mistake (. to ? in dice file)

src/about_dice_project.rb

@@ -56,7 +56,7 @@ class AboutDiceProject < Neo::Koan
     #
     # If the rolls are random, then it is possible (although not
     # likely) that two consecutive rolls are equal.  What would be a
-    # better way to test this.
+    # better way to test this?
   end
 
   def test_you_can_roll_different_numbers_of_dice