chore: bump to newer nightly (#1426)

tokio-executor/src/global.rs

@@ -153,7 +153,7 @@ where
         // when leaving the scope. This handles cases that involve panicking.
         struct Reset<'a>(&'a Cell<State>, State);
 
-        impl<'a> Drop for Reset<'a> {
+        impl Drop for Reset<'_> {
             fn drop(&mut self) {
                 self.0.set(self.1);
             }

tokio-executor/tests/enter.rs

@@ -1,5 +1,5 @@
 #![warn(rust_2018_idioms)]
-#![feature(await_macro, async_await)]
+#![feature(async_await)]
 
 #[test]
 fn block_on_ready() {

tokio-executor/tests/executor.rs

@@ -1,5 +1,5 @@
 #![warn(rust_2018_idioms)]
-#![feature(await_macro, async_await)]
+#![feature(async_await)]
 
 use tokio_executor::{self, DefaultExecutor};