Add cask for Google Music Manager.
user
```ruby
class GoogleMusicManager < Cask
  url 'https://dl.google.com/dl/androidjumper/mac/718015/musicmanager.dmg'
  homepage 'https://music.google.com'
  version '1.0.71.8015'
  sha1 '1f695cb8b08606476a3a12acd86a0a2d36da81a5'
  link 'MusicManager.app'
end
```
assistant