CloudServices class should destroy token class on self-destroy, and token class should stop refreshing on self-destroy. Otherwise, token won't stop refreshing after editor destroy.
Thanks, @oskarwrobel! I forgot to implement it.
Note that we should not use protected _stopRefreshing. Instead, this class should have public destroy method.
I just wrote it ~ 1-2 minutes ago https://github.com/ckeditor/ckeditor-cloudservices-core/issues/9 :D