Update to 1.3.6d
    
    - New upstream release 1.3.6d
      - Fixed issue with FTPS uploads of large files using TLSv1.3
        (https://github.com/proftpd/proftpd/issues/959)
      - Fixed regression in the handling of '%{env:...}' configuration variables
        when the environment variable is not present
        (https://github.com/proftpd/proftpd/issues/857)
      - Second LIST of the same symlink shows different results
        (https://github.com/proftpd/proftpd/issues/940)
      - mod_sftp sends broken response when CREATETIME attribute is requested
        (https://github.com/proftpd/proftpd/issues/980)
      - Handle zero-length SFTP WRITE requests without error
        (http://bugs.proftpd.org/show_bug.cgi?id=4398)
      - PidFile should not be world-writable
        (https://github.com/proftpd/proftpd/issues/1018)
      - TLSv1.3 handshake fails due to missing session ticket key on some systems
        (https://github.com/proftpd/proftpd/issues/1014)
      - Lowercased FTP commands not properly identified
        (https://github.com/proftpd/proftpd/issues/1023)