tokio: re-export future/stream utils (#1387)

tokio/examples/udp-codec.rs

@@ -9,15 +9,15 @@
 #![feature(async_await)]
 #![deny(warnings, rust_2018_idioms)]
 
+use tokio::io;
+use tokio::net::UdpSocket;
+use tokio::prelude::*;
+
 use std::env;
 use std::error::Error;
 use std::net::SocketAddr;
 use std::time::Duration;
 
-use tokio::io;
-use tokio::net::UdpSocket;
-use tokio::util::FutureExt;
-
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn Error>> {
     let _ = env_logger::init();