Adding to SSH Known Hosts

Travis CI can add entries to ~/.ssh/known_hosts prior to cloning your git repository, which is necessary if there are git submodules from domains other than github.com, gist.github.com, or ssh.github.com.

Both hostnames and IP addresses are supported, as the keys are added via ssh-keyscan. A single host may be specified like so:

addons:
  ssh_known_hosts: git.example.com

Multiple hosts or IPs may be added as a list:

addons:
  ssh_known_hosts:
  - git.example.com
  - 111.22.33.44