Bump pillow from 5.2.0 to 6.2.0 in /demo_and_tests

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>

demo_and_tests/requirements.txt

@@ -1,4 +1,4 @@
 Django==2.1
 django-formtools>=1.0
 django-nose>=1.4
-Pillow==5.2.0
+Pillow==6.2.0