message: docs(server): doc test of `Builder` to async future
diff: @@ -378,26 +378,28 @@ impl<I, E> Builder<I, E> {
  /// # Example
  ///
  /// ```
  - /// # extern crate hyper;
  + /// # #![feature(async_await)]
  + /// # #[cfg(not(feature = "runtime"))]
  /// # fn main() {}
  /// # #[cfg(feature = "runtime")]
  - /// # fn run() {
  - /// use hyper::{Body, Response, Server};
  - /// use hyper::service::service_fn_ok;
  + /// # #[hyper::rt::main]
  + /// # async fn main() {
  + /// use hyper::{Body, Error, Response, Server};
  + /// use hyper::service::{make_service_fn, service_fn};
  ///
  /// // Construct our SocketAddr to listen on...
  /// let addr = ([127, 0, 0, 1], 3000).into();
  ///
  - /// // And a NewService to handle each connection...
  - /// let new_service = || {
  - /// service_fn_ok(|_req| {
  - /// Response::new(Body::from("Hello World"))
  - /// })
  - /// };
  + /// // And a MakeService to handle each connection...
  + /// let make_svc = make_service_fn(|_| async {
  + /// Ok::<_, Error>(service_fn(|_req| async {
  + /// Ok::<_, Error>(Response::new(Body::from("Hello World")))
  + /// }))
  + /// });
  ///
  /// // Then bind and serve...
  /// let server = Server::bind(&addr)
  - /// .serve(new_service);
  + /// .serve(make_svc);
  ///
  /// // Finally, spawn `server` onto an Executor...
  /// # }
  