自动部署Let’s Encrypt证书时出现以下故障，求解。

Missing command line flags. For non-interactive execution, you will need to specify a plugin on the command line.  Run with '--help plugins' to see a list of options, and see https://eff.org/letsencrypt-plugins for more detail on what the plugins do and how to use them.
系统为ubuntu16.04。
提示安装成功，但是添加网站时不会出现是否使用Let’s Encrypt证书的选项。