Bump pillow from 7.1.0 to 8.1.1 in /requirements

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>

requirements/requirements-base.txt

@@ -2,6 +2,6 @@ Kivy==2.0.0rc2
 Kivy-Garden==0.1.4
 numpy==1.18.4
 opencv-python==4.2.0.34
-Pillow==7.1.0
+Pillow==8.1.1
 pyzbar==0.1.8
 xcamera==2019.928