Bump nltk from 3.8.1 to 3.9

Bumps [nltk](https://github.com/nltk/nltk) from 3.8.1 to 3.9.
- [Changelog](https://github.com/nltk/nltk/blob/develop/ChangeLog)
- [Commits](nltk/nltk@3.8.1...3.9)

---
updated-dependencies:
- dependency-name: nltk
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

docs/requirements.txt

@@ -46,7 +46,7 @@ matplotlib==3.8.2
     # via niapy
 niapy==2.1.0
     # via -r requirements.in
-nltk==3.8.1
+nltk==3.9
     # via -r requirements.in
 numpy==1.26.4
     # via