Close context to ensure that logging system is cleaned up

See gh-6688

spring-boot-samples/spring-boot-sample-logback/src/main/java/sample/logback/SampleLogbackApplication.java

 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,7 +37,7 @@ public class SampleLogbackApplication {
 	}
 
 	public static void main(String[] args) throws Exception {
-		SpringApplication.run(SampleLogbackApplication.class, args);
+		SpringApplication.run(SampleLogbackApplication.class, args).close();
 	}
 
 }