Fix a deprecation warning

Author: alexcrichton

src/lib.rs

@@ -114,12 +114,12 @@ impl Drop for Bomb {
 mod lock {
     use std::boxed::Box;
     use std::cell::Cell;
-    use std::sync::{Mutex, MutexGuard, Once, ONCE_INIT};
+    use std::sync::{Mutex, MutexGuard, Once};
 
     pub struct LockGuard(Option<MutexGuard<'static, ()>>);
 
     static mut LOCK: *mut Mutex<()> = 0 as *mut _;
-    static INIT: Once = ONCE_INIT;
+    static INIT: Once = Once::new();
     thread_local!(static LOCK_HELD: Cell<bool> = Cell::new(false));
 
     impl Drop for LockGuard {