Have `hackage` mirror use HTTPS

This commit changes the URLs in the definition of the `hackage` mirror
to use HTTPS rather than unsecured HTTP.

The changed URLs refer to the domains `hackage.haskell.org` and
`dev.gentoo.org`, which are covered by HTTPS certificates issued by
generally-accepted certificate authorities (GlobalSign and DigiCert,
respectively); hence, I believe that this should be a safe change to
make.

Signed-off-by: 8573 <8573dd@gmail.com>