Do not test nightly's debug format
diff --git a/tests/test.rs b/tests/test.rs
index 7acd6c3..6a06092 100644
--- a/tests/test.rs
+++ b/tests/test.rs
@@ -329,6 +329,7 @@
 }
 
 #[test]
+#[cfg(not(feature = "nightly"))]
 fn test_debug_tokenstream() {
     let tts = TokenStream::from_str("[a + 1]").unwrap();