Update Wicket API link to nightlies version

Author: martin-g

pom.xml

@@ -1317,7 +1317,7 @@
 							'The code being documented uses modules
 							but the packages defined in https://docs.oracle.com/javaee/7/api/ are
 							in the unnamed module.'-->
-							<link>https://ci.apache.org/projects/wicket/apidocs/9.x</link>
+							<link>https://nightlies.apache.org/wicket/apidocs/9.x</link>
 							<link>https://docs.spring.io/spring/docs/5.1.x/javadoc-api</link>
 							<link>https://www.slf4j.org/apidocs</link>
 						</links>