Update README.md

Author: gkorland

README.md

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 # RedisJSON Python Client
 
-[![Mailing List](https://img.shields.io/badge/Mailing%20List-RedisJSON-blue)](https://groups.google.com/forum/#!forum/redisjson)
+[![Forum](https://img.shields.io/badge/Forum-RedisJSON-blue)](https://forum.redislabs.com/c/modules/redisjson)
 [![Gitter](https://badges.gitter.im/RedisLabs/RedisJSON.svg)](https://gitter.im/RedisLabs/RedisJSON?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
 
 rejson-py is a package that allows storing, updating and querying objects as