fix doc for UnixStream

Author: mlowicki

library/std/src/os/unix/net/stream.rs

@@ -307,11 +307,11 @@ impl UnixStream {
     ///
     /// ```no_run
     /// use std::io;
-    /// use std::net::UdpSocket;
+    /// use std::os::unix::net::UnixStream;
     /// use std::time::Duration;
     ///
     /// fn main() -> std::io::Result<()> {
-    ///     let socket = UdpSocket::bind("127.0.0.1:34254")?;
+    ///     let socket = UnixStream::connect("/tmp/sock")?;
     ///     let result = socket.set_write_timeout(Some(Duration::new(0, 0)));
     ///     let err = result.unwrap_err();
     ///     assert_eq!(err.kind(), io::ErrorKind::InvalidInput);