Bump pillow from 5.4.1 to 6.2.0

Bumps [pillow](https://github.com/python-pillow/Pillow) from 5.4.1 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@5.4.1...6.2.0)

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

requirements.txt

@@ -19,7 +19,7 @@ MarkupSafe==1.1.0
 mccabe==0.6.1
 more-itertools==5.0.0
 packaging==18.0
-Pillow==5.4.1
+Pillow==6.2.0
 pipdeptree==0.13.2
 pkginfo==1.5.0.1
 pluggy==0.8.1