docker-compose: remove obsolete version setting
diff --git a/korap4dnb-compose.yml b/korap4dnb-compose.yml
index b64c530..9743285 100644
--- a/korap4dnb-compose.yml
+++ b/korap4dnb-compose.yml
@@ -1,4 +1,3 @@
-version: '3.8'
 volumes:
   example-index:
 services: