Update CHANGELOG

CHANGELOG.md

@@ -25,6 +25,8 @@ IMPROVEMENTS:
     specified for `vagrant box list` [GH-2327]
   - core: Multiple SSH keys can be specified with `config.ssh.private_key_path`
     [GH-907]
+  - commands/box/add: Can now specify a client cert when downloading a
+    box. [GH-1889]
   - commands/init: Add `--output` option for specifing output path, or
     "-" for stdin. [GH-1364]
   - commands/provision: Add `--no-parallel` option to disable provider