Update README.md

Signed-off-by: Vlad Volkov <vlad@hiberbee.com>

Author: vladyslavvolkov

README.md

@@ -12,7 +12,7 @@ services:
       POSTGRES_PASSWORD: password
 
   backup:
-    image: ghcr.io/hiberbee/postgres-backup-s3:18.0
+    image: ghcr.io/hiberbee/postgres-backup-s3:18
     environment:
       SCHEDULE: '@weekly'     # optional
       BACKUP_KEEP_DAYS: 7     # optional