Requirement.txt need to checked with also python versions

[niladricts]

There are so many flaws in requirements.txt. The python libraries that are mentioned in the file specially nltk, pattern needs python3.5+. Quite curious to know-how then it is written in the python version requirements: python2.7.x? It should be python 3.5.x to make all consistencies. Here are the nltk requirements:

https://pypi.org/project/nltk/