heroku nltk.txt code example

Example: nltk in heroku

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