fix spring config

spring-security-core/src/main/java/org/baeldung/app/App.java

@@ -3,6 +3,7 @@ package org.baeldung.app;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.boot.autoconfigure.domain.EntityScan;
+import org.springframework.boot.web.support.SpringBootServletInitializer;
 import org.springframework.context.annotation.ComponentScan;
 import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
 
@@ -10,7 +11,7 @@ import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
 @EnableJpaRepositories("org.baeldung.repository")
 @ComponentScan("org.baeldung")
 @EntityScan("org.baeldung.entity")
-public class App {
+public class App extends SpringBootServletInitializer {
     public static void main(String[] args) {
         SpringApplication.run(App.class, args);
     }