Add Prezi for Mac v5.1.1
user
```ruby
class Prezi < Cask
  url 'https://prezi-a.akamaihd.net/desktop/Prezi5.1.1.dmg'
  homepage 'http://www.prezi.com/'
  version '5.1.1'
  sha256 'cd77adf228b237f24407a4a7c8e57463b27ad98d9885451e42cc7416484cce56'
  link 'Prezi.app'
end
```
assistant