Bump pillow from 3.3.2 to 8.1.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 3.3.2 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@3.3.2...8.1.1)

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

Author: dependabot[bot]

pip-requirements.txt

@@ -78,7 +78,7 @@ pathlib2==2.2.1
 pbr==3.1.1
 pexpect==4.0.1
 pickleshare==0.7.4
-Pillow==3.3.2
+Pillow==8.1.1
 piston-mini-client==0.7.5
 plac==0.9.6
 polyglot==16.7.4