Add 'Debug' to 'Responder' derive in announcement.

site/news/2018-12-08-version-0.4.md

@@ -287,7 +287,7 @@ Alternatively, an `enum` could be declared with the appropriate variants, and
 implementation can be automatically derived:
 
 ```rust
-#[derive(Responder)]
+#[derive(Responder, Debug)]
 enum Error {
     #[response(status = 401)]
     Unauthorized(Json<Info>),