set sonar-maven-plugin version

without that Maven build complains that the 'build.plugins.plugin.version'a
for org.sonarsource.scanner.maven:sonar-maven-plugin is missing and
"future Maven versions might no longer support building such malformed projects."

Author: vladak

pom.xml

@@ -456,6 +456,7 @@ Portions Copyright (c) 2018, 2020, Chris Fraire <[email protected]>.
               <plugin>
                 <groupId>org.sonarsource.scanner.maven</groupId>
                 <artifactId>sonar-maven-plugin</artifactId>
+                <version>3.9.1.2184</version>
               </plugin>
             </plugins>
           </build>