This is caused by a down-age of Github raw file link.
Meanwhile a stop-gap solution would be to manually download the file:
PATH_TO_NLTK_DATA=/home/username/nltk_data/
wget https://github.com/nltk/nltk_data/archive/gh-pages.zip
unzip gh-pages.zip
mv nltk_data-gh-pages/ $PATH_TO_NLTK_DATA
We’re working on finding an alternative to the data and model downloading.
Meanwhile, @everyone please help to check that your script(s) and make sure that you’re not overloading the data downloads! Thank you in advance!!
Please check https://github.com/nltk/nltk/issues/1787 for latest updates on this issue.