pip install --upgrade pip或 使用pip安装一些包时，出现SSL证书相关问题
Cache entry deserialization failed, entry ignored
Could not fetch URL https://pypi.tuna.tsinghua.edu.cn/simple/tensorflow/: There was a problem confirming the ssl certificate: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:748) - skipping找了很多方法，其实在后面加入下面参数就可以
-i http://pypi.douban.com/simple/ --trusted-host pypi.douban.com完整
pip install --upgrade pip -i http://pypi.douban.com/simple/ --trusted-host pypi.douban.com