Bump django from 1.11.20 to 1.11.23

Bumps [django](https://github.com/django/django) from 1.11.20 to 1.11.23.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@1.11.20...1.11.23)

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

requirements-doc.txt

@@ -10,7 +10,7 @@ certifi==2019.3.9         # via requests
 chardet==3.0.4            # via requests
 coreapi==2.3.3            # via django-rest-swagger, openapi-codec
 coreschema==0.0.4         # via coreapi
-django==1.11.20
+django==1.11.23
 django-bootstrap3==9.1.0  # via shuup
 django-countries==5.2     # via shuup
 django-enumfields==0.9.0  # via shuup