Autocomplete via MetaCPAN over HTTPS

Otherwise Firefox (at least v31.0) blocks the request because
rt.cpan.org is served over HTTPS.  Chrome was unaffected.

Reported on perl5-porters in
<CA+vYcVxy+DLJfs1XDVabrMrOqBxwis4dDX7PGQMBd_x_grPMxQ@mail.gmail.com>