Bump nltk from 3.0.0 to 3.4.5

Bumps [nltk](https://github.com/nltk/nltk) from 3.0.0 to 3.4.5.
- [Release notes](https://github.com/nltk/nltk/releases)
- [Changelog](https://github.com/nltk/nltk/blob/develop/ChangeLog)
- [Commits](nltk/nltk@3.0.0...3.4.5)

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

Author: dependabot[bot]

requirements.txt

@@ -1 +1 @@
-nltk==3.0.0
+nltk==3.4.5