Bump ecdsa from 0.11 to 0.13.3

Bumps [ecdsa](https://github.com/warner/python-ecdsa) from 0.11 to 0.13.3.
- [Release notes](https://github.com/warner/python-ecdsa/releases)
- [Changelog](https://github.com/warner/python-ecdsa/blob/python-ecdsa-0.13.3/NEWS)
- [Commits](https://github.com/warner/python-ecdsa/compare/python-ecdsa-0.11...python-ecdsa-0.13.3)

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

requirements.txt

@@ -8,7 +8,7 @@ kombu==3.0.35
 billiard==3.3.0.23
 Markdown==2.4
 djangorestframework==3.4.7
-ecdsa==0.11
+ecdsa==0.13.3
 Pygments==1.6
 django-filter==0.15.2
 jsonfield==0.9.22