title: Error while installing virtualenv using pip on Windows
body: <p>Trying to install virtualenv using pip on windows machine but facing below error</p>
  
  <pre><code>pip install virtualenv
      Collecting virtualenv
      Exception:
      Traceback (most recent call last): File "c:\python27\lib\site-packages\pip\basecommand.py", line 215, in main status = self.run(options, args)
      File "c:\python27\lib\site-packages\pip\commands\install.py", line 324, in run
      requirement_set.prepare_files(finder)
      File "c:\python27\lib\site-packages\pip\req\req_set.py", line 380, in prepare_files ignore_dependencies=self.ignore_dependencies))
      File "c:\python27\lib\site-packages\pip\req\req_set.py", line 620, in _prepare_file session=self.session, hashes=hashes)
      File "c:\python27\lib\site-packages\pip\download.py", line 821, in unpack_url hashes=hashes
      File "c:\python27\lib\site-packages\pip\download.py", line 659, in unpack_http_url hashes)
      File "c:\python27\lib\site-packages\pip\download.py", line 853, in _download_http_url stream=True,
      File "c:\python27\lib\site-packages\pip\_vendor\requests\sessions.py", line 488, in get return self.request('GET', url, **kwargs)
      File "c:\python27\lib\site-packages\pip\download.py", line 386, in request return super(PipSession, self).request(method, url, *args, **kwargs)
      File "c:\python27\lib\site-packages\pip\_vendor\requests\sessions.py", line 475, in request resp = self.send(prep, **send_kwargs)
      File "c:\python27\lib\site-packages\pip\_vendor\requests\sessions.py", line 596, in send r = adapter.send(request, **kwargs)
      File "c:\python27\lib\site-packages\pip\_vendor\cachecontrol\adapter.py", line 47, in send resp = super(CacheControlAdapter, self).send(request, **kw)
      File "c:\python27\lib\site-packages\pip\_vendor\requests\adapters.py", line 497, in send raise SSLError(e, request=request)
      SSLError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:661)
      You are using pip version 9.0.1, however version 10.0.1 is available.
      You should consider upgrading via the 'python -m pip install --upgrade pip' command.
  </code></pre>