Add OnyX cask for Snow Leopard
user
```ruby
class OnyxSnowleopard < Cask
  url 'http://www.titanium.free.fr/download/106/OnyX.dmg'
  homepage 'http://www.titanium.free.fr/downloadonyx.php'
  version '2.4.0'
  sha1 '5aea8cf00bd77eff95ea875daecad0183eb03871'
  link 'OnyX.app'
end
```
assistant