This update for proftpd fixes the following issues:

proftpd was updated to 1.3.6d:

* Issue 857 - Fixed regression in the handling of `%{env:...}` configuration
  variables when the environment variable is not present. 
* Issue 940 - Second LIST of the same symlink shows different results.
* Issue 959 - FTPS uploads using TLSv1.3 are likely to fail unexpectedly.
* Issue 980 - mod_sftp sends broken response when CREATETIME attribute is
  requested.
* Bug 4398 - Handle zero-length SFTP WRITE requests without error.
* Issue 1018 - PidFile should not be world-writable.
* Issue 1014 - TLSv1.3 handshake fails due to missing session ticket key on
  some systems.
* Issue 1023 - Lowercased FTP commands not properly identified.