Add 'private' to type

This commit is dirty but works for me.

I have a private repo which I want to use tachikoma to. but

* `https://` requires login name and password
* `ssh://` doesn't require them (if ssh key is set) but tachikoma doesn't support

so I add 'private' to type in order to support `ssh://`.

If you set `"ssh://github.com/user_name/private_repo.git"` to url, it work.