Sub-communities filter does not include private communities

https://www.topcoder.com/challenges? User : picachui User is part of topgear, zuruich and CS sub-communities, but they are not listed in the dropdown

<img width="1440" alt="Screenshot 2020-08-24 at 4 12 30 PM" src="https://user-images.githubusercontent.com/58783823/91036329-c4038e80-e624-11ea-807a-7798bccd8d5e.png">

Final Submission Guidelines

Git issue link: https://github.com/topcoder-platform/community-app/issues/4806