Update README.md

Co-authored-by: Alexander Makarov <[email protected]>

README.md

@@ -47,7 +47,7 @@ docker run --rm --name yiisoft-cache-memcached-cache --detach --publish 11211:11
 Memcached must be accessible by address `127.0.0.1`. If you use PHP via docker container, run PHP container in network
 of memcached container. Use `docker run` command argument for it:
 
-```dockerfile
+```shell
 --network container:yiisoft-cache-memcached-cache
 ```