Bump django-s3sign from 0.4.0 to 0.5.1

Bumps [django-s3sign](https://github.com/ccnmtl/django-s3sign) from 0.4.0 to 0.5.1.
- [Release notes](https://github.com/ccnmtl/django-s3sign/releases)
- [Changelog](https://github.com/ccnmtl/django-s3sign/blob/master/CHANGES)
- [Commits](ccnmtl/django-s3sign@0.4.0...0.5.1)

---
updated-dependencies:
- dependency-name: django-s3sign
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements.txt

@@ -126,7 +126,7 @@ django-storages==1.14.6
 django-cacheds3storage==0.3.0
 django-markwhat==1.6.2
 
-django-s3sign==0.4.0
+django-s3sign==0.5.1
 django-smtp-ssl==1.0
 
 ctlsettings==0.4.4