Create Onyx cask for Mountain Lion
user
```ruby
class OnyxMountainlion < Cask
  url 'http://joel.barriere.pagesperso-orange.fr/dl/108/OnyX.dmg'
  homepage 'http://www.titanium.free.fr/downloadonyx.php'
  version '2.7.4'
  sha1 'dadd7f82fd972e73a7a8e360583b8d4d7963482c'
  link 'OnyX.app'
end
```
assistant