Fixed a comment, to reflect changes in the task.

The task has a test with a missing comma.  That same comma is missing in the comment, so I'm putting it here as well.

1-js/05-data-types/05-array-methods/12-reduce-object/task.md

@@ -23,7 +23,7 @@ let usersById = groupById(users);
 // after the call we should have:
 
 usersById = {
-  john: {id: 'john', name: "John Smith", age: 20}
+  john: {id: 'john', name: "John Smith", age: 20},
   ann: {id: 'ann', name: "Ann Smith", age: 24},
   pete: {id: 'pete', name: "Pete Peterson", age: 31},
 }