Bump m-site-plugin to 3.21.0

Author: slachiewicz

pom.xml

@@ -41,6 +41,7 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-site-plugin</artifactId>
+          <version>3.21.0</version>
           <configuration>
             <topSiteURL>scm:git:[email protected]:codehaus-plexus</topSiteURL>
           </configuration>