punkt install instruction from README fails

[gregelin]

Gregs-MacBook-Pro:compliancekbs greg$ python3 -m nltk.downloader punkt
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/runpy.py:125: RuntimeWarning: 'nltk.downloader' found in sys.modules after import of package 'nltk', but prior to execution of 'nltk.downloader'; this may result in unpredictable behaviour
  warn(RuntimeWarning(msg))
[nltk_data] Error loading punkt: <urlopen error [SSL:
[nltk_data]     CERTIFICATE_VERIFY_FAILED] certificate verify failed
[nltk_data]     (_ssl.c:777)>