Bump pillow from 2.2.2 to 8.1.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 2.2.2 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@2.2.2...8.1.1)

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

Author: dependabot[bot]

requirements.txt

@@ -7,7 +7,7 @@ matplotlib==3.3.3
 networkx==2.5
 numpy==1.19.4
 opencv-python==3.2.0.8
-Pillow==2.2.2
+Pillow==8.1.1
 pkg-resources==0.0.0
 pyparsing==2.4.7
 python-dateutil==2.8.1