Python安装selenium及报错原因

C:\Users\88304>pip --default-timeout=100 install -U selenium==2.53.6
Collecting selenium==2.53.6
  Downloading https://files.pythonhosted.org/packages/3f/f8/e46684764161fee7b7d2e0fd9b82d56915438b68e498181dc45183643c82/selenium-2.53.6-py2.py3-none-any.whl (884kB)
     |████████████████████████████████| 890kB 297kB/s
Installing collected packages: selenium
Successfully installed selenium-2.53.6