Use correct method

Closes #4120

Author: coke

doc/Type/Iterable.pod6

@@ -74,7 +74,7 @@ Note that the flattening is recursive, so C<((("a", "b"), "c"),
 "d").flat> returns C<("a", "b", "c", "d")>, but it does not flatten
 itemized sublists:
 
-    say ($('a', 'b'), 'c').raku;    # OUTPUT: «($("a", "b"), "c")␤»
+    say ($('a', 'b'), 'c').flat;    # OUTPUT: «($("a", "b"), "c")␤»
 
 You can use the L«hyper method call|/language/operators#index-entry-methodop_>>.» to
 call the L«C<.List>|/routine/List» method on all the inner itemized sublists