Log Message:
libssh: update to 0.91.

version 0.9.1 (released 2019-10-25)
  * Added support for Ed25519 via OpenSSL
  * Added support for X25519 via OpenSSL
  * Added support for localuser in Match keyword
  * Fixed Match keyword to be case sensitive
  * Fixed compilation with LibreSSL
  * Fixed error report of channel open (T75)
  * Fixed sftp documentation (T137)
  * Fixed known_hosts parsing (T156)
  * Fixed build issue with MinGW (T157)
  * Fixed build with gcc 9 (T164)
  * Fixed deprecation issues (T165)
  * Fixed known_hosts directory creation (T166)