Upgrade antora-ui-spring to 0.4.13.

Author: OlgaMaciaszek

docs/antora-playbook.yml

@@ -37,4 +37,4 @@ runtime:
     format: pretty
 ui:
   bundle:
-    url: https://github.com/spring-io/antora-ui-spring/releases/download/v0.4.11/ui-bundle.zip
+    url: https://github.com/spring-io/antora-ui-spring/releases/download/v0.4.13/ui-bundle.zip