Support ssh-ed25519 SSH keys

Summary: Fixes T7121.

Test Plan: Used `ssh-keygen -t ed25519` on an Ubuntu 14 box to generate a key; verified this is the header on the corresponding public key.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7121

Differential Revision: https://secure.phabricator.com/D11930

src/applications/auth/sshkey/PhabricatorAuthSSHPublicKey.php

@@ -59,6 +59,7 @@ final class PhabricatorAuthSSHPublicKey extends Phobject {
       'ssh-dsa',
       'ssh-dss',
       'ssh-rsa',
+      'ssh-ed25519',
       'ecdsa-sha2-nistp256',
       'ecdsa-sha2-nistp384',
       'ecdsa-sha2-nistp521',