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] <support@github.com>

requirements.txt

@@ -4,7 +4,7 @@ django-markdown-deux==1.0.5
 django-pagedown==1.0.5
 django-widget-tweaks==1.4.2
 markdown2==2.3.5
-Pillow==5.1.0
+Pillow==6.2.0
 gunicorn
 djangorestframework
 whitenoise==3.0