Bump django-simple-captcha from 0.5.18 to 0.5.20

Bumps [django-simple-captcha](https://github.com/mbi/django-simple-captcha) from 0.5.18 to 0.5.20.
- [Changelog](https://github.com/mbi/django-simple-captcha/blob/master/CHANGES)
- [Commits](mbi/django-simple-captcha@v0.5.18...v0.5.20)

---
updated-dependencies:
- dependency-name: django-simple-captcha
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

requirements/tarballs.txt

@@ -1,6 +1,6 @@
 # these do not provide wheel packages
 
-django-simple-captcha==0.5.18
+django-simple-captcha==0.5.20
 django-vinaigrette==2.0.1
 python-bugzilla==3.2.0
 uWSGI==2.0.22