Bump idna from 2.7 to 3.7

Bumps [idna](https://github.com/kjd/idna) from 2.7 to 3.7.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.rst)
- [Commits](kjd/idna@v2.7...v3.7)

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

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

requirements.txt

@@ -169,7 +169,7 @@ enum34==1.1.10
 funcsigs==1.0.2
 future==0.18.3
 futures==3.3.0
-idna==2.7
+idna==3.7
 ipaddress==1.0.23
 libsass==0.20.1
 ndg-httpsclient==0.5.1