requirements.txt has two versions of nltk

[andw99]

The file GODEL/requirements.txt lists two versions of nltk

line 6: nltk==3.7
line 19: nltk==3.4.1

Resulting in:

• ERROR: Cannot install nltk==3.4.1 and nltk==3.7 because these package versions have conflicting dependencies.
• ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/topics/dependency-resolution/#dealing-with-dependency-conflicts

[ba2512005]

@andw99 Based on the PR's just use the latest version and remove the older version.