Update Perl6 docset

[novaTopFlex]

Since about 2019, the Perl 6 specification has been renamed to the "Raku" specification. Much of the specification overall should remain similar to the earlier "Perl6" specification otherwise.

[lshprung]

It looks like Hans-J. Schmid contributed the Perl6 docset, but the link to his Github account is a 404. In order to get a more up to date Perl6 docset, someone will have to take over as maintainer and either recover Schmid's docset generator or create a new docset generator.