fix(server): Make sleep_on_errors configurable and use it in example

examples/hello.rs

@@ -19,7 +19,10 @@ fn main() {
             .with_body(PHRASE))
     }));
 
-    let server = Http::new().bind(&addr, new_service).unwrap();
+    let server = Http::new()
+        .sleep_on_errors(true)
+        .bind(&addr, new_service)
+        .unwrap();
     println!("Listening on http://{} with 1 thread.", server.local_addr().unwrap());
     server.run().unwrap();
 }