build(deps): bump flask-cors from 3.0.4 to 3.0.8

Bumps [flask-cors](https://github.com/corydolphin/flask-cors) from 3.0.4 to 3.0.8.
- [Release notes](https://github.com/corydolphin/flask-cors/releases)
- [Changelog](https://github.com/corydolphin/flask-cors/blob/master/CHANGELOG.md)
- [Commits](corydolphin/flask-cors@3.0.4...3.0.8)

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

requirements.txt

@@ -6,7 +6,7 @@ chardet==3.0.4
 click==6.7
 -e git+https://github.com/flxwu/contest.io.git@0c3474fc8c7134d803631690fa44bcd97a5c07f3#egg=contest.io
 Flask==1.0.2
-Flask-Cors==3.0.4
+Flask-Cors==3.0.8
 Flask-Migrate==2.1.1
 Flask-SQLAlchemy==2.3.2
 GitHub-Flask==3.2.0