Bump idna from 2.6 to 3.7

Bumps [idna](https://github.com/kjd/idna) from 2.6 to 3.7.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.rst)
- [Commits](kjd/idna@v2.6...v3.7)

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

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

requirements.txt

@@ -7,7 +7,7 @@ djangorestframework==3.11.2
 entrypoints==0.3
 flake8==3.7.9
 gunicorn==19.8.1
-idna==2.6
+idna==3.7
 mccabe==0.6.1
 oauthlib==2.1.0
 psycopg2-binary==2.7.7