Bump pillow from 5.3.0 to 8.1.1 in /docker/torch-notebook

Bumps [pillow](https://github.com/python-pillow/Pillow) from 5.3.0 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@5.3.0...8.1.1)

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

Author: dependabot[bot]

docker/torch-notebook/requirements.txt

@@ -1,5 +1,5 @@
 torchvision==0.7
-Pillow==5.3.0
+Pillow==8.1.1
 Flask==1.0.2
 numpy==1.16.2
 pandas==0.24.2