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>

Author: dependabot[bot]

requirements-3.txt

@@ -7,7 +7,7 @@ chardet==3.0.4
 clint==0.5.1
 docutils==0.15.2
 freezegun==1.2.2
-idna==2.7
+idna==3.7
 linecache2==1.0.0
 mypy==1.7.1
 packaging==16.8