Bump pillow from 7.1.2 to 8.1.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 7.1.2 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@7.1.2...8.1.1)

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

requirements.txt

@@ -7,6 +7,6 @@ pandas==0.23.3
 scikit_image==0.15.0
 numpy==1.14.3
 torch==1.2.0
-Pillow==7.1.2
+Pillow==8.1.1
 scikit_learn==0.22.2.post1
 skimage==0.0