我正在尝试在代理之后的ubuntu 18.04中安装docker ce。我已经添加了gpg密钥，并且在我的sourcs.list文件中，docker条目看起来像这样：
deb [arch=amd64 trusted=yes] http://download.docker.com/linux/ubuntu bionic stable
deb-src [arch=amd64 trusted=yes] http://download.docker.com/linux/ubuntu bionic stable
我已经通过首先在另一个系统上下载，然后移动到当前系统，然后添加apt-key来安装密钥。
在运行sudo apt-get update时出现错误：
Failed to fetch https://download.docker.com/linux/ubuntu/dists/bionic/stable/source/Sources Certificate verification failed: The certificate is NOT trusted. The certificate issuer is unknown. Could not handshake: Error in the certificate verification. [IP: xx.xx.xx.xx xxxx] (proxy address)