具体错误：ERROR: Cannot uninstall 'PyYAML'. It is a distutils installed project and thus we cannot accurately determine which files belong to it which would lead to only a partial uninstall.
原因：环境中已经存在某个版本的PyYAML，因此简单的pip指令并不能更新或者删除该包
解决方案：忽略已安装的PYYAML包，重新安装
指令：pip install PyYAML --ignore-installed
最终成功更新PyYAML到最新版本，结果如下图所示：
