Update events.adoc

Changes type to DefaultAuthenticationEventPublisher

Only DefaultAuthenticationEventPublisher has the method
setDefaultAuthenticationFailureEvent, but not the interface
AuthenticationEventPublisher.

docs/modules/ROOT/pages/servlet/authentication/events.adoc

@@ -143,7 +143,7 @@ Java::
 @Bean
 public AuthenticationEventPublisher authenticationEventPublisher
         (ApplicationEventPublisher applicationEventPublisher) {
-    AuthenticationEventPublisher authenticationEventPublisher =
+    DefaultAuthenticationEventPublisher authenticationEventPublisher =
         new DefaultAuthenticationEventPublisher(applicationEventPublisher);
     authenticationEventPublisher.setDefaultAuthenticationFailureEvent
         (GenericAuthenticationFailureEvent.class);