fix spring config (#2374)

* fix spring config

* fix spring config

spring-mvc-email/src/main/java/com/baeldung/spring/Application.java

@@ -2,10 +2,11 @@ package com.baeldung.spring;
 
 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);
     }