Bump pillow from 6.2.1 to 8.1.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 6.2.1 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@6.2.1...8.1.1)

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

Author: dependabot[bot]

requirements.txt

@@ -55,7 +55,7 @@ oauthlib==3.1.0
 packaging==19.1
 pandas==0.25.1
 parse==1.12.1
-Pillow==6.2.1
+Pillow==8.1.1
 pip-date==1.0.3
 pip-review==1.0
 pipenv==2018.11.26