Bump pillow from 7.2.0 to 8.1.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 7.2.0 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@7.2.0...8.1.1)

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

Author: dependabot[bot]

requirements.txt

@@ -1,3 +1,3 @@
 Django==2.2.17
-Pillow==7.2.0
+Pillow==8.1.1
 pytz==2020.1