Update django-s3sign requirement from <=0.2.1 to <=0.4.0

Updates the requirements on [django-s3sign](https://github.com/ccnmtl/django-s3sign) to permit the latest version.
- [Release notes](https://github.com/ccnmtl/django-s3sign/releases)
- [Changelog](https://github.com/ccnmtl/django-s3sign/blob/master/CHANGES)
- [Commits](ccnmtl/django-s3sign@0.1.4...0.4.0)

---
updated-dependencies:
- dependency-name: django-s3sign
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -114,7 +114,7 @@ django-storages==1.14.2
 ctlsettings==0.3.2
 funcsigs==1.0.2
 pbr==6.0.0
-django-s3sign<=0.2.1
+django-s3sign<=0.4.0
 django-smtp-ssl==1.0
 
 pbr==6.0.0