'nltk.downloader' found in sys.modules after import of package 'nltk', but prior to execution of 'nltk.downloader';
You need to follow the below steps.

nltk.txt needs to present at the root folder
Add the modules you want to download like punkt, stopwords as separate row items
Change the line ending from windows to UNIX.

Changing the line ending is a very important step. Can be easily done through Sublime Text or Notepad++.
In Sublime Text, it can done from the View menu, then Line Endings.
Hope this helps
I have developed a NLTK based flask app. Now I have deployed it in Heorku. While deploying it I am getting an error: remote: /app/.heroku/python/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. And also some pages and functions are not working properly. Please suggest me something to solve this problem.