Made class final as the only constructor has private modifier

git-svn-id: http://svn.us.apache.org/repos/asf/tuscany@723726 13f79535-47bb-0310-9956-ffa450edef68

java/sca/modules/extensibility/src/main/java/org/apache/tuscany/sca/extensibility/ServiceDiscovery.java

@@ -31,7 +31,7 @@ import java.util.logging.Logger;
  *
  * @version $Rev$ $Date$
  */
-public class ServiceDiscovery implements ServiceDiscoverer {
+public final class ServiceDiscovery implements ServiceDiscoverer {
     private static final Logger logger = Logger.getLogger(ServiceDiscovery.class.getName());
 
     private final static ServiceDiscovery INSTANCE = new ServiceDiscovery();