fix(iterators1): reorder TODO steps

Update the TODO steps in the iterators1 exercise.

exercises/standard_library_types/iterators1.rs

@@ -18,7 +18,7 @@ fn main () {
     assert_eq!(my_iterable_fav_fruits.next(), Some(&"banana"));
     assert_eq!(my_iterable_fav_fruits.next(), ???);     // TODO: Step 2
     assert_eq!(my_iterable_fav_fruits.next(), Some(&"avocado"));
-    assert_eq!(my_iterable_fav_fruits.next(), ???);     // TODO: Step 2.1
-    assert_eq!(my_iterable_fav_fruits.next(), Some(&"raspberry"));
     assert_eq!(my_iterable_fav_fruits.next(), ???);     // TODO: Step 3
+    assert_eq!(my_iterable_fav_fruits.next(), Some(&"raspberry"));
+    assert_eq!(my_iterable_fav_fruits.next(), ???);     // TODO: Step 4
 }