Log Message:
security/ruby-sshkit: update to 1.21.2

1.21.2 (2021-01-18)

Bug Fixes

* Fix closed connection in pool (#487) @azrle

Documentation

* Update EXAMPLES.md to show how to set the ssh user (#485) @bretweinraub

Housekeeping

* Add latest rubies to CI, including 3.0; drop rubinius CI support (#489)
  @mattbrictson