Update sphinx from 2.0.1 to 2.1.0 (#649)
Update sphinx from 2.0.1 to 2.1.0 (#649)

(no need to wait for codecov)
django-json-api/django-rest-framework-json-api,django-json-api/django-rest-framework-json-api,django-json-api/rest_framework_ember,leo-naeka/django-rest-framework-json-api