The python request url failed due to the lack of ca certificate

My ci script will download package from the host of www.nuget.org, but it failed due to the lack of ca certificate

  Traceback (most recent call last):
        File "..\deps\windows-install.py", line 22, in <module>
          filedata = urllib2.urlopen(librdkafkaNugetUrl)
        File "C:\ProgramData\chocolatey\lib\mingw\tools\install\mingw64\opt\lib\python2.7/urllib2.py", line 154, in urlopen
          return opener.open(url, data, timeout)
        File "C:\ProgramData\chocolatey\lib\mingw\tools\install\mingw64\opt\lib\python2.7/urllib2.py", line 431, in open
          response = self._open(req, data)
        File "C:\ProgramData\chocolatey\lib\mingw\tools\install\mingw64\opt\lib\python2.7/urllib2.py", line 449, in _open
          '_open', req)
        File "C:\ProgramData\chocolatey\lib\mingw\tools\install\mingw64\opt\lib\python2.7/urllib2.py", line 409, in _call_chain
          result = func(*args)
        File "C:\ProgramData\chocolatey\lib\mingw\tools\install\mingw64\opt\lib\python2.7/urllib2.py", line 1240, in https_open
          context=self._context)
        File "C:\ProgramData\chocolatey\lib\mingw\tools\install\mingw64\opt\lib\python2.7/urllib2.py", line 1197, in do_open
          raise URLError(err)
    urllib2.URLError : <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:581)> 

The entire log contains such error is : https://travis-ci.org/yunnysunny/node-rdkafka/jobs/504583885

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