upgrade antora-ui-spring

Author: christophstrobl

src/main/antora/antora-playbook.yml

@@ -36,5 +36,5 @@ runtime:
     format: pretty
 ui:
   bundle:
-    url: https://github.com/spring-io/antora-ui-spring/releases/download/v0.4.16/ui-bundle.zip
+    url: https://github.com/spring-io/antora-ui-spring/releases/download/v0.4.18/ui-bundle.zip
     snapshot: true