Django 下载pillow 出错WARNING: You are using pip version 19.2.3, however version 20.1 is available.

在Django中以python -m pip install Pillow命令下载pillow，总是出现以下问题：
ERROR: Could not find a version that satisfies the requirement Pillow (from versions: none)
ERROR: No matching distribution found for Pillow
WARNING: You are using pip version 19.2.3, however version 20.1 is available.
You should consider upgrading via the ‘python -m pip install --upgrade pip’ command.

根据提示执行了python -m pip install --upgrade pip 命令以后，依旧出现
WARNING: You are using pip version 19.2.3, however version 20.1 is available.
You should consider upgrading via the ‘python -m pip install --upgrade pip’

解决办法是：直接执行以下命令下载

python -m pip install -U Pillow

虽然这个问题还在，但这时pillow已经安装好了，如果要解决这个警告问题，需要更新pip版本。