Modify to use the ConfigurableApplicationContext in reference document

Issue: SPR-13000

src/asciidoc/core-beans.adoc

@@ -3212,19 +3212,19 @@ singleton beans so that all resources are released. Of course, you must still co
 and implement these destroy callbacks correctly.
 
 To register a shutdown hook, you call the `registerShutdownHook()` method that is
-declared on the `AbstractApplicationContext` class:
+declared on the `ConfigurableApplicationContext` interface:
 
 [source,java,indent=0]
 [subs="verbatim,quotes"]
 ----
-	import org.springframework.context.support.AbstractApplicationContext;
+	import org.springframework.context.ConfigurableApplicationContext;
 	import org.springframework.context.support.ClassPathXmlApplicationContext;
 
 	public final class Boot {
 
 		public static void main(final String[] args) throws Exception {
 
-			AbstractApplicationContext ctx = new ClassPathXmlApplicationContext(
+			ConfigurableApplicationContext ctx = new ClassPathXmlApplicationContext(
 					new String []{"beans.xml"});
 
 			// add a shutdown hook for the above context...