Bump pillow from 7.1.0 to 8.1.1 in /algo-dev-demo/digits-recognition/src

Bumps [pillow](https://github.com/python-pillow/Pillow) from 7.1.0 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@7.1.0...8.1.1)

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

Author: dependabot[bot]

algo-dev-demo/digits-recognition/src/requirements.txt

@@ -2,4 +2,4 @@ algorithmia>=1.0.0,<2.0
 numpy==1.19.4
 scipy==1.5.3
 scikit-learn==0.23.2
-pillow==7.1.0
+pillow==8.1.1