Fix Unix signal registration to use try_into()

Author: taiki-e

examples/unix-signal.rs

@@ -8,15 +8,15 @@
 
 #[cfg(unix)]
 fn main() -> std::io::Result<()> {
-    use std::os::unix::{io::AsRawFd, net::UnixStream};
+    use std::os::unix::net::UnixStream;
 
     use async_io::Async;
     use futures_lite::{future, prelude::*};
 
     future::block_on(async {
         // Create a Unix stream that receives a byte on each signal occurrence.
         let (a, mut b) = Async::<UnixStream>::pair()?;
-        signal_hook::low_level::pipe::register_raw(signal_hook::consts::SIGINT, a.as_raw_fd())?;
+        signal_hook::low_level::pipe::register_raw(signal_hook::consts::SIGINT, a.try_into()?)?;
         println!("Waiting for Ctrl-C...");
 
         // Receive a byte that indicates the Ctrl-C signal occurred.