Bump pillow from 8.3.0 to 8.3.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 8.3.0 to 8.3.1.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@8.3.0...8.3.1)

---
updated-dependencies:
- dependency-name: pillow
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

requirements.txt

@@ -4,7 +4,7 @@ scipy==1.7.0
 matplotlib==3.4.2
 scikit-learn>=0.22.2,<0.24.3
 six==1.16.0
-Pillow==8.3.0
+Pillow==8.3.1
 tqdm==4.61.2
 statsmodels==0.12.2
 pydub==0.25.1