Bump pillow from 5.2.0 to 6.2.0

Bumps [pillow](https://github.com/python-pillow/Pillow) from 5.2.0 to 6.2.0.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@5.2.0...6.2.0)

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

Author: dependabot[bot]

requirements.txt

@@ -7,7 +7,7 @@ scipy==1.1.0
 tensorflow==1.15.0
 grpcio==1.14.1
 jupyter_core==4.4.0
-Pillow==5.2.0
+Pillow==6.2.0
 GitPython==2.1.11
 grpc==0.3-19
 imageio==2.3.0