Let unix_socket example compile but not run on Windows (#849)

* Let `unix_socket` example compile but not run on Windows

examples/unix_socket.rs

@@ -1,10 +1,11 @@
 #![deny(warnings)]
 
-use tokio::net::UnixListener;
-use tokio_stream::wrappers::UnixListenerStream;
-
+#[cfg(unix)]
 #[tokio::main]
 async fn main() {
+    use tokio::net::UnixListener;
+    use tokio_stream::wrappers::UnixListenerStream;
+
     pretty_env_logger::init();
 
     let listener = UnixListener::bind("/tmp/warp.sock").unwrap();
@@ -13,3 +14,9 @@ async fn main() {
         .run_incoming(incoming)
         .await;
 }
+
+#[cfg(not(unix))]
+#[tokio::main]
+async fn main() {
+    panic!("Must run under Unix-like platform!");
+}