Bump pillow from 6.2.0 to 8.1.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 6.2.0 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@6.2.0...8.1.1)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 numpy==1.17.2
 pandas==0.25.1
-Pillow==6.2.0
+Pillow==8.1.1
 matplotlib==3.1.1
 pickleshare==0.7.5