PostfixAdmin was updated to 2.3.8 to deliver bugs fixed upstream.

* don't prefill username in users/ login on failed logins - fixes (probably harmless) XSS
* properly escape mail addresses in query (#356)
* fix escaping in create-admin, create-mailbox and fetchmail templates
* fixes (harmless) XSS on form validation errors
* don't echo the password back to the browser in the fetchmail form
* enforce minimum password length in create-mailbox