fix artifact of migration to traefik

roles/pretix_docker/tasks/main.yml

@@ -95,9 +95,9 @@
     - pretix-db.service
     - pretix-redis.service
     
-- name: "Add Pretix to Docker network nginx_net"
+- name: "Add Pretix to Docker network traefik"
   docker_network:
-    name: nginx_net
+    name: traefik
     connected:
       - "{{ pretix_container_name }}"
     appends: true