Suppress some deprecation warnings in the doc tests

These cause failures in CI.  I can't reproduce them locally and don't
know why.

Author: asomers

src/sys/aio.rs

@@ -1080,6 +1080,7 @@ pub fn aio_suspend(
 /// This mode is useful for otherwise-synchronous programs that want to execute
 /// a handful of I/O operations in parallel.
 /// ```
+/// # #![allow(deprecated)]
 /// # use std::os::unix::io::AsRawFd;
 /// # use nix::sys::aio::*;
 /// # use nix::sys::signal::SigevNotify;
@@ -1104,6 +1105,7 @@ pub fn aio_suspend(
 /// technique for reducing overall context-switch overhead, especially when
 /// combined with kqueue.
 /// ```
+/// # #![allow(deprecated)]
 /// # use std::os::unix::io::AsRawFd;
 /// # use std::thread;
 /// # use std::time;
@@ -1137,6 +1139,7 @@ pub fn aio_suspend(
 /// In that case, you must check the status of each individual operation, and
 /// possibly resubmit some.
 /// ```
+/// # #![allow(deprecated)]
 /// # use libc::c_int;
 /// # use std::os::unix::io::AsRawFd;
 /// # use std::sync::atomic::{AtomicBool, Ordering};