当直接输入python -m pip install --upgrade pip更新还报错的时候，
输入命令：python -m pip install -U pip

Collecting pip
Downloading https://files.pythonhosted.org/packages/f9/fb/863012b13912709c13cf5cfdbfb304fa6c727659d6290438e1a88df9d848/pip-19.1-py2.py3-none-any.whl (1.4MB)
100% |████████████████████████████████| 1.4MB 21kB/s
Installing collected packages: pip
Found existing installation: pip 19.0.3
Uninstalling pip-19.0.3:
Successfully uninstalled pip-19.0.3
Successfully installed pip-19.1