Bump pillow from 2.9.0 to 8.1.1 in /requirements

Bumps [pillow](https://github.com/python-pillow/Pillow) from 2.9.0 to 8.1.1.
- [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/2.9.0...8.1.1)

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

requirements/requirements.txt

@@ -11,7 +11,7 @@ easy-thumbnails==2.2
 eav-django==1.4.7
 gunicorn==19.3.0
 html5lib==0.9999999
-Pillow==2.9.0
+Pillow==8.1.1
 pisa==3.0.33
 psycopg2==2.6.1
 python-memcached==1.53