Bump nltk from 3.4.4 to 3.4.5 (#135)

Bumps [nltk](https://github.com/nltk/nltk) from 3.4.4 to 3.4.5.
- [Release notes](https://github.com/nltk/nltk/releases)
- [Changelog](https://github.com/nltk/nltk/blob/develop/ChangeLog)
- [Commits](https://github.com/nltk/nltk/compare/3.4.4...3.4.5

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements.txt

@@ -7,7 +7,7 @@ fuzzywuzzy==0.17.0
 lxml==4.4.1
 matplotlib==2.2.4
 numpy==1.16.4
-nltk==3.4.4
+nltk==3.4.5
 Pillow>=3.4.1
 python-crfsuite==0.9.6
 Pyqtree==1.0.0