Bump requests from 2.20.1 to 2.21.0 (#213)

Bumps [requests](https://github.com/requests/requests) from 2.20.1 to 2.21.0.
- [Release notes](https://github.com/requests/requests/releases)
- [Changelog](https://github.com/kennethreitz/requests/blob/master/HISTORY.md)
- [Commits](psf/requests@v2.20.1...v2.21.0)

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

Author: dependabot[bot]

homeassistant_cli/package_constraints.txt

@@ -10,7 +10,7 @@ cryptography==2.3.1
 pip>=8.0.3
 pytz>=2018.07
 pyyaml>=4.2b1
-requests==2.20.1
+requests==2.21.0
 ruamel.yaml==0.15.78
 voluptuous==0.11.5
 voluptuous-serialize==2.1.0