Upgrade locksmithctl to version 0.2.2

Version 0.2.2 supports the `-endpoint` flag to specify an etcd client
URL:
https://github.com/coreos/locksmith/commit/e3fe40126e3e5ff3d350be116c6f136e007b65c5#diff-3ceac677474a0ac6dbeeba6c665ebf75
Merge pull request #81 from alphagov/73607174-upgrade_locksmith

[#73607174] Upgrade locksmithctl to version 0.2.2