change config flags from ssr to server to match the features

packages/fullstack/examples/axum-hello-world/src/main.rs

@@ -51,7 +51,7 @@ fn main() {
     #[cfg(feature = "web")]
     tracing_wasm::set_as_global_default();
 
-    #[cfg(feature = "ssr")]
+    #[cfg(feature = "server")]
     tracing_subscriber::fmt::init();
 
     launch(app);