解决You are using pip version 8.1.2, however version 20.0.2 is available. You should consider upgradin

解决You are using pip version 8.1.2, however version 20.0.2 is available.
You should consider upgrading via the ‘python -m pip install --upgrade pip’ command.

以下这3种方法我通通都不行

python -m pip install --upgrade pip
pip install --upgrade pip --force-reinstall
python -m pip install -U pip

解决方法：

python -m pip install -i https://pypi.tuna.tsinghua.edu.cn/simple --upgrade pip