Add cask for Air Video Server
user
```ruby
class AirVideoServer < Cask
  url 'http://s3.amazonaws.com/AirVideo/Air+Video+Server+2.4.6-beta3u1.dmg'
  homepage 'http://www.inmethod.com/air-video/'
  version '2.4.6-beta3'
  sha1 '2293b653fea6a939ab863a7bf918d601a504c9c8'
end
```
assistant