Support Mail Service Provider Postmark in flarum

Tutorial

Thanks to https://github.com/wildbit/swiftmailer-postmark
Add PostmarkTransport.php which locate in "flarum/vendor/illuminate/mail/Transport/" and Modify TransportManager.php which locate in "flarum/vendor/illuminate/mail/"
In your administration, in email block, setting like this:
1. Driver: postmark
  1. Encryption: Your-postmark-server-token
  2. Sender: email in Postmark Sender Signatures List

My gist: