Onyx: Fix Mavericks/Mountain Lion and add Tiger/Leopard download links

Matches links seen here: http://www.titanium.free.fr/onyx.html
I (naively) assumed the Yosemite link would be valid, should've checked it too, my bad.  I'm not sure of the protocol for homebrew-cask here, though.  The **correct** link, as given on the website, is http://www.titanium.free.fr/download/1010/OnyX.dmg (*download* instead of *dl* in the cask file), although the link you give @jawshooah clearly works and also follows the same pattern as the others; md5 hashes are the same.  Is priority given to the link matching the obviously-preferred pattern or the link given on the actual website?