Can't link to libdl on freebsd

[moon-chilled]

On freebsd, I get an error because there's no libdl. The functionality provided by libdl is superseded by libc there, so you can just leave out the requirement. Can you fix this? I would make a PR but I don't yet know all the ins and outs of dub.json.

[jtbx]

To remove the dependency on libdl, remove line 15 of dub.json.

If you are still encountering this issue, that is. ;)