[Security] Bump feedgen from 0.8.0 to 0.9.0

Bumps [feedgen](https://github.com/lkiesow/python-feedgen) from 0.8.0 to 0.9.0. **This update includes a security fix.**
- [Release notes](https://github.com/lkiesow/python-feedgen/releases)
- [Commits](lkiesow/python-feedgen@v0.8.0...v0.9.0)

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

requirements.txt

@@ -19,7 +19,7 @@ django-storages==1.7.2
 djangorestframework==3.10.3
 # dnspython3==1.15.0
 facebook-sdk==3.1.0
-feedgen==0.8.0
+feedgen==0.9.0
 feedparser==5.2.1
 gunicorn==19.9.0
 kombu==4.6.5