Update to 1.3.8
    
    - New upstream release 1.3.8
      - 1.3.8rc4 failed to build mod_sftp with OpenSSL 1.1.0 due to X448 check
        (GH#1488)
      - 1.3.8rc4 failed to build on Solaris due to missing type declarations
        (GH#1494)
      - mod_ifsession doesn't change the effect of SFTPMaxChannels (GH#1500)
      - mod_tls module unexpectedly allows TLS handshake after authentication in
        some configurations (GH#1533)
      - Disable FSCachePolicy by default (GH#1528)
      - Avoid logging "session closed" messages unless there is a corresponding
        "session opened" log message, to avoid user confusion (GH#1539)
      - Implement support for the CSID FTP command (GH#1550)
      - Unable to verify signed data: signature type 'rsa-sha2-512' does not match
        publickey algorithm 'ssh-rsa' (Bug #4491)
      - mod_auth_otp improperly allows keyboard-interactive logins for users
        lacking OTP entries (GH#1560)
    - Update mod_vroot to 0.9.11
      - Addresses a bad interaction with mod_auth_file, and failed login attempts,
        which can lead to inexplicably "stuck" processes that cannot be terminated
        (https://github.com/proftpd/proftpd/issues/1384)
    - Use SPDX-format license tag