Bump flask-cors from 3.0.8 to 3.0.9

Bumps [flask-cors](https://github.com/corydolphin/flask-cors) from 3.0.8 to 3.0.9.
- [Release notes](https://github.com/corydolphin/flask-cors/releases)
- [Changelog](https://github.com/corydolphin/flask-cors/blob/master/CHANGELOG.md)
- [Commits](corydolphin/flask-cors@3.0.8...3.0.9)

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

Author: dependabot[bot]

flask-server/requirements.txt

@@ -7,7 +7,7 @@ dialogflow==0.7.2
 entrypoints==0.3
 flake8==3.7.9
 Flask==1.1.1
-Flask-Cors==3.0.8
+Flask-Cors==3.0.9
 google-api-core==1.16.0
 google-auth==1.11.0
 googleapis-common-protos==1.51.0