docs(aio): Fix http guide

aio/content/guide/http.md

@@ -335,7 +335,7 @@ If you have a need to mutate the request body, you need to copy the request body
 Since requests are immutable, they cannot be modified directly. To mutate them, use `clone()`:
 
 ```javascript
-intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpError<any>> {
+intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
   // This is a duplicate. It is exactly the same as the original.
   const dupReq = req.clone();