Add 4K Video Downloader cask
user
```ruby
class FourkVideoDownloader < Cask
  url 'http://4kdownload.googlecode.com/files/4kvideodownloader_2.8.dmg'
  homepage 'http://www.4kdownload.com/products/product-videodownloader'
  version '2.8'
  sha1 'f0e78400574b9291ed8ad271d51d231d2d9f3e11'
  link '4K Video Downloader.app'
end
```
assistant