pip 安装 python 包时，报错：You are using pip version 7.1.2, however version 19.3.1 is available. You should
pip 安装 python 包时，报错：You are using pip version 7.1.2, however version 19.3.1 is available. You should consider upgrading via the 'python -m pip install --upgrade pip' command.
解决方法，进入 python 的安装目录，运行 python -m pip install --upgrade pip