前言：用pip安装wordcloud时提示：WARNING: You are using pip version 19.2.3, however version 20.2.3 is available.
于是开始升级pip（python -m pip install --upgrade pip），结果报错 Consider using the `--user` option or check the permissions.
解决办法：运行python -m ensurepip，后再运行python -m pip install --upgrade pip，之后便可安装wordcloud了
