chore: bump to newer nightly (#1485)

tokio-timer/src/interval.rs

@@ -77,8 +77,6 @@ impl Interval {
     /// # Examples
     ///
     /// ```
-    /// #![feature(async_await)]
-    ///
     /// use tokio::timer::Interval;
     ///
     /// use std::time::Duration;

tokio-timer/src/lib.rs

@@ -6,7 +6,6 @@
     unreachable_pub
 )]
 #![doc(test(no_crate_inject, attr(deny(rust_2018_idioms))))]
-#![feature(async_await)]
 
 //! Utilities for tracking time.
 //!

tokio-timer/src/timeout.rs

@@ -32,8 +32,6 @@ use std::time::{Duration, Instant};
 /// example:
 ///
 /// ```rust,no_run
-/// #![feature(async_await)]
-///
 /// use tokio::prelude::*;
 /// use tokio::sync::mpsc;
 ///
@@ -96,8 +94,6 @@ impl<T> Timeout<T> {
     /// Create a new `Timeout` set to expire in 10 milliseconds.
     ///
     /// ```rust
-    /// #![feature(async_await)]
-    ///
     /// use tokio::timer::Timeout;
     /// use tokio::sync::oneshot;
     ///