当我尝试使用 sudo apt-get update 时，出现以下错误：
E: The repository 'http://de.archive.ubuntu.com/ubuntu zesty Release' does no longer have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
我该怎么做才能正确更新 Ubuntu？
我在 Ubuntu 17.04
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