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](https://github.com/python-pillow/Pillow/compare/5.2.0...6.2.0)
Signed-off-by: Ndependabot[bot] <support@github.com>

requirements.txt

@@ -11,7 +11,7 @@ Markdown==3.0.1
 matplotlib==2.2.3
 numpy==1.15.1
 opencv-python==3.4.3.18
-Pillow==5.2.0
+Pillow==6.2.0
 protobuf==3.6.1
 pyparsing==2.2.0
 python-dateutil==2.7.3