Java Version set to 1.8

anonymous types replaced by lambda's
Method references used instead of Lambda's
Explicit type replaced by <>
travis.yml updated to java 1.8

broker/src/main/java/io/moquette/server/Server.java

@@ -75,14 +75,8 @@ public class Server {
         final Server server = new Server();
         server.startServer();
         System.out.println("Server started, version 0.10-SNAPSHOT");
-        // Bind a shutdown hook
-        Runtime.getRuntime().addShutdownHook(new Thread() {
-
-            @Override
-            public void run() {
-                server.stopServer();
-            }
-        });
+        //Bind  a shutdown hook
+        Runtime.getRuntime().addShutdownHook(new Thread(server::stopServer));
     }
 
     /**