Bump pillow from 5.4.1 to 6.2.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 5.4.1 to 6.2.1.
- [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/5.4.1...6.2.1

)

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

requirements.txt

@@ -43,7 +43,7 @@ gunicorn==19.9.0
 mailchimp3==3.0.9
 mistune==0.8.4
 more-itertools==7.2.0
-Pillow==5.4.1
+Pillow==6.2.1
 psycopg2==2.7.3.1
 social_auth_app_django==3.1.0
 tomd==0.1.3