add missing redis env var to docker-compose file

docker-compose.yml

@@ -99,6 +99,7 @@ services:
       - CLIENT_URL=http://localhost:3000
       - GATEWAY_URL=http://localhost:8080/api
       - CONTENT_FETCH_URL=http://content-fetch:8080/?token=some_token
+      - REDIS_URL='redis://redis:6379'
     depends_on:
       migrate:
         condition: service_completed_successfully