Use version 18

Author: sbrunner

docker-compose.yaml

@@ -1,7 +1,7 @@
 services:
   geoserver:
     # Credentials: admin/geoserver
-    image: georchestra/geoserver:20.0.x
+    image: georchestra/geoserver:18.06
     volumes:
       - ./examples/geoserver-data/:/mnt/geoserver_datadir
       - ./core/src/test/resources/map-data/:/mnt/geoserver_datadir/www/map-data