Bump pillow from 5.1.0 to 6.2.0

Bumps [pillow](https://github.com/python-pillow/Pillow) from 5.1.0 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@5.1.0...6.2.0)

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

Author: dependabot[bot]

requirements_stub.txt

@@ -25,7 +25,7 @@ MarkupSafe==1.0
 numpy==1.14.3
 opencv-contrib-python==3.4.3.18
 pigpio==1.40.post1
-Pillow==5.1.0
+Pillow==6.2.0
 protobuf==3.6.1
 Pypubsub==4.0.0
 pytz==2018.4