Remove superfluous 'for' in example

Author: sjn

lib/Language/functions.pod

@@ -232,7 +232,7 @@ supplies: they can come as L<multis|#Multi-dispatch>,
 you can L<wrap|/type/Routine#method wrap> them, and exit early with C<return>:
 
 =begin code :allow<B>
-my $keywords = set <if for unless while for>;
+my $keywords = set <if for unless while>;
 
 sub has-keyword(*@words) {
     for @words -> $word {