Bump idna from 2.8 to 3.7 (#227)

Bumps [idna](https://github.com/kjd/idna) from 2.8 to 3.7.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.rst)
- [Commits](kjd/idna@v2.8...v3.7)

---
updated-dependencies:
- dependency-name: idna
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements-frozen.txt

@@ -10,7 +10,7 @@ django-mptt==0.11.0
 django-page-cms==2.0.11
 django-taggit==1.2.0
 djangorestframework==3.15.2
-idna==2.8
+idna==3.7
 isort==4.3.21
 lazy-object-proxy==1.4.3
 Markdown==3.2.1