tokio-xmpp: Run rustfmt on that one example

It started breaking CI for some reason, probably a rustfmt update.

tokio-xmpp/examples/download_avatars.rs

@@ -235,7 +235,10 @@ fn handle_iq_result(pubsub: PubSub, from: &Jid) {
 fn save_avatar(from: &Jid, id: String, data: &[u8]) -> io::Result<()> {
     let directory = format!("data/{}", from);
     let filename = format!("data/{}/{}", from, id);
-    println!("Saving avatar from {} to {}.", from, filename);
+    println!(
+        "Saving avatar from {} to {}.",
+        from, filename
+    );
     create_dir_all(directory)?;
     let mut file = File::create(filename)?;
     file.write_all(data)