[pom] Bump site to 3.21.0

Author: hazendaz

pom.xml

@@ -348,7 +348,7 @@
     <rewrite.plugin>5.46.1</rewrite.plugin>
     <scm-publish.plugin>3.3.0</scm-publish.plugin>
     <shade.plugin>3.6.0</shade.plugin>
-    <site.plugin>4.0.0-M16</site.plugin>
+    <site.plugin>3.21.0</site.plugin>
     <sonar.plugin>5.0.0.4389</sonar.plugin>
     <sortpom.plugin>4.0.0</sortpom.plugin>
     <source.plugin>3.3.1</source.plugin>