Add Cask for Postgres.app version 9.3.1.0-alpha1
user
```ruby
class PostgresApp < Cask
  url 'https://github.com/PostgresApp/PostgresApp/releases/download/9.3.1.0-alpha1/Postgres93.zip'
  homepage 'http://postgresapp.com/'
  version '9.3.1.0-alpha1'
  sha1 'fa2c504fd791564484995226dd339b5b9eaa2519'
  link 'Postgres93.app'
end
```
assistant