Update ArcWaker::into_waker() call

Syntax of cuntion has been changed
See rust-lang/futures-rs#1676

src/webcore/executor.rs

@@ -8,7 +8,7 @@
 use futures_core::future::{FutureObj, LocalFutureObj};
 use futures_executor::enter;
 use futures_core::task::{Spawn, SpawnError};
-use futures_util::task::ArcWake;
+use futures_util::task::{self, ArcWake};
 use std::future::Future;
 use std::task::{Poll, Context};
 use std::pin::Pin;
@@ -71,7 +71,7 @@ impl Task {
 
         let poll = {
             // TODO is there some way of saving these so they don't need to be recreated all the time ?
-            let waker = ArcWake::into_waker( arc.clone() );
+            let waker = task::waker( arc.clone() );
             let cx = &mut Context::from_waker( &waker );
 
             // TODO what if poll panics ?