Add Xmarks for Safari cask
user
```ruby
class XmarksSafari < Cask
 url 'https://static.xmarks.com/clients/safari/xmarks_for_safari_2.0.11.dmg'
 homepage 'http://www.xmarks.com/'
 version '2.0.11'
 sha1 'eae9ce0865bf1d4a3e6a2ff020793b36efdf1b51'
 install 'Xmarks for Safari Installer.pkg'
end
```
assistant