Bump pillow from 7.1.0 to 8.1.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 7.1.0 to 8.1.1.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@7.1.0...8.1.1)

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

Author: dependabot[bot]

requirements.txt

@@ -6,7 +6,7 @@ nltk==3.4.5
 numpy==1.18.0
 opencv-contrib-python==4.1.2.30
 opencv-python==4.1.2.30
-Pillow==7.1.0
+Pillow==8.1.1
 pyparsing==2.4.6
 python-dateutil==2.8.1
 six==1.13.0