Update answer key for sets addition.

src/path_to_answer_sheet.clj

@@ -28,7 +28,8 @@
                     :jelly
                     :jelly
                     [:butter :and]]}
-   "sets" {"__" [#{1 2 3 4 5}
+   "sets" {"__" [0
+                 #{1 2 3 4 5}
                  #{1 2 3 4 5}
                  #{2 3}
                  #{1 4}]}