各位大牛,在 centos7 中安装 letsencrypt 证书时遇到这个错误怎么解决？

错误代码是

Replacing certbot-auto... Creating virtual environment... Installing Python packages... Traceback (most recent call last): File "/tp/tmp.BZ7PbBwAvJ/pipstrap.py", line 177, in <module> sys.exit(main()) File "/tmp/tmp.BZ7PbBwAvJ/pipstrap.py", line 158, in main for path, digest in PACKAGES] File "/tmp/tmp.BZ7PbBwAvJ/pipstrap.py", line 117, in hashed_download respOnse= opener(using_https=parsed_url.scheme == 'https').open(url) File "/usr/lib64/python2.7/urllib2.py", line 437, in open respOnse= meth(req, response) File "/usr/lib64/python2.7/urllib2.py", line 550, in http_response 'http', request, response, code, msg, hdrs) File "/usr/lib64/python2.7/urllib2.py", line 469, in error result = self._call_chain(*args) File "/usr/lib64/python2.7/urllib2.py", line 409, in _call_chain result = func(*args) File "/usr/lib64/python2.7/urllib2.py", line 656, in http_error_302 return self.parent.open(new, timeout=req.timeout) File "/usr/lib64/python2.7/urllib2.py", line 437, in open respOnse= meth(req, response) File "/usr/lib64/python2.7/urllib2.py", line 550, in http_response 'http', request, response, code, msg, hdrs) File "/usr/lib64/python2.7/urllib2.py", line 469, in error result = self._call_chain(*args) File "/usr/lib64/python2.7/urllib2.py", line 409, in _call_chain result = func(*args) File "/usr/lib64/python2.7/urllib2.py", line 656, in http_error_302 return self.parent.open(new, timeout=req.timeout) File "/usr/lib64/python2.7/urllib2.py", line 431, in open respOnse= self._open(req, data) File "/usr/lib64/python2.7/urllib2.py", line 449, in _open '_open', req) File "/usr/lib64/python2.7/urllib2.py", line 409, in _call_chain result = func(*args) File "/usr/lib64/python2.7/urllib2.py", line 1258, in https_open cOntext=self._context, check_hostname=self._check_hostname) File "/usr/lib64/python2.7/urllib2.py", line 1214, in do_open raise URLError(err) urllib2.URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:618)> 

应该怎么解决？