Fixed node_async documentation example

Author: lemunozm

src/node.rs

@@ -376,7 +376,7 @@ impl<S: Send + 'static> NodeListener<S> {
     /// handler.signals().send_with_timer((), std::time::Duration::from_secs(1));
     /// let (id, addr) = handler.network().listen(Transport::FramedTcp, "127.0.0.1:0").unwrap();
     ///
-    /// let task = listener.for_each(move |event| match event {
+    /// let task = listener.for_each_async(move |event| match event {
     ///      NodeEvent::Network(net_event) => { /* Your logic here */ },
     ///      NodeEvent::Signal(_) => handler.stop(),
     /// });