Bump idna from 2.8 to 2.9

Bumps [idna](https://github.com/kjd/idna) from 2.8 to 2.9.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.rst)
- [Commits](kjd/idna@v2.8...v2.9)

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

requirements.txt

@@ -13,7 +13,7 @@ dockerflow==2019.10.0
 ec2_metadata==2.1.0
 hawkauthlib==2.0.0
 hupper==1.9.1
-idna==2.8
+idna==2.9
 iso8601==0.1.12
 jsonpatch==1.25
 jsonpointer==2.0