Fix some final errors

Cargo.toml

@@ -37,7 +37,7 @@ pin-utils = "0.1.0-alpha.4"
 slab = "0.4.2"
 
 [dependencies.futures-preview]
-version = "0.3.0-alpha.17"
+version = "0.3.0-alpha.18"
 features = ["async-await", "nightly"]
 
 [dev-dependencies]

docs/src/tutorial/all_together.md

@@ -135,18 +135,6 @@ async fn broker(mut events: Receiver<Event>) -> Result<()> {
     }
     Ok(())
 }
-
-fn spawn_and_log_error<F>(fut: F) -> task::JoinHandle<()>
-where
-    F: Future<Output = Result<()>> + Send + 'static,
-{
-    task::spawn(async move {
-        if let Err(e) = fut.await {
-            eprintln!("{}", e)
-        }
-    })
-}
-
 ```
 
 1. Inside the `server`, we create the broker's channel and `task`.

docs/src/tutorial/sending_messages.md

@@ -19,7 +19,6 @@ if Alice and Charley send two messages to Bob at the same time, Bob will see the
 #     net::TcpStream,
 #     prelude::Stream,
 # };
-# use std::sync::Arc;
 use futures::channel::mpsc; // 1
 use futures::SinkExt;
 use std::sync::Arc;