fix spring config

spring-security-client/spring-security-thymeleaf-authentication/src/main/java/org/baeldung/config/Application.java

@@ -2,9 +2,10 @@ package org.baeldung.config;
 
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.web.support.SpringBootServletInitializer;
 
 @SpringBootApplication
-public class Application {
+public class Application extends SpringBootServletInitializer {
 
     public static void main(String[] args) {
         SpringApplication.run(Application.class, args);