Python：pip install 报错SSL: CERTIFICATE_VERIFY_FAILED

不用在意具体安装的是什么。总之，报错了。红色的地方。
pip install 名字
Collecting virtualenv
/opt/python27/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:315: SNIMissingWarning: An HTTPS request has been made, but the SNI (Subject Name Indication) extension to TLS is not available on this platform. This may cause the server to present an incorrect TLS certificate, which can cause validation failures. For more information, see https://urllib3.readthedocs.org/en/latest/security.html#snimissingwarning.   SNIMissingWarning
  Could not fetch URL https://pypi.python.org/simple/virtualenv/: There was a problem confirming the ssl certificate: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590) - skipping
  Could not find a version that satisfies the requirement virtualenv (from versions: )
百度到了，这么写。
pip --trusted-host pypi.python.org install 名字