output for "unique n-grams" is weird

since you're printing out the `.sort` of a Set, you'll get a list of pairs that all have `True` as the value

consider using `.unique.sort` instead of `.Set.sort`

```
perl6 -e 'my $n=2; say "banana".comb.rotor($n => 1 - $n)».join.unique.sort'
(an ba na)
```