问题描述：
WARNING: You are using pip version 19.2.3, however version 20.0.2 is available.即使是警告，还是下载不了第三方库
根据提示，进行pip的平滑升级
pip install --upgrade pip
又报错？
ERROR: Could not install packages due to an EnvironmentError: [Errno 13] Permission denied: '/usr/bin/pip'
Consider using the `--user` option or check the permissions.
解决：加上user后成功～～
pip install --user --upgrade pip
