chore(deps): update traefik docker tag to v2.8.4

Author: renovate[bot]

docker-compose/src/docker/docker-compose.yml

@@ -266,7 +266,7 @@ services:
       - traefik.http.services.mailserver-service.loadbalancer.server.port=1080
 
   reverse-proxy:
-    image: traefik:v2.8.3
+    image: traefik:v2.8.4
     command:
       - --entrypoints.http.address=:8080
       - --entrypoints.https.address=:8443