Bump idna from 2.8 to 3.7

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>

requirements.txt

@@ -37,7 +37,7 @@ google >= 1.7
 html5lib==1.0.1
 httplib2==0.19.1
 i18n==0.2
-idna==2.8
+idna==3.7
 importlib-metadata==1.5.0
 jeepney==0.8.0
 jsonschema==3.2.0