久しぶりに vagrant を使うので、 box を update しようとしたら変なエラーが出た。
$ vagrant box outdated --global
* 'ubuntu/xenial64': Error loading metadata: The requested URL returned error: 404 Not Found
* 'ubuntu/trusty64': Error loading metadata: The requested URL returned error: 404 Not Found
* 'centos/6': Error loading metadata: The requested URL returned error: 404 Not Found
* 'centos/7': Error loading metadata: The requested URL returned error: 404 Not Found