Rename `unstable` feature to `nightly`
diff --git a/tests/test.rs b/tests/test.rs
index 6442ba6..8320876 100644
--- a/tests/test.rs
+++ b/tests/test.rs
@@ -6,7 +6,7 @@
 use proc_macro2::TokenNode;
 
 #[cfg(procmacro2_unstable)]
-#[cfg(not(feature = "unstable"))]
+#[cfg(not(feature = "nightly"))]
 use proc_macro2::Span;
 
 #[test]
@@ -121,7 +121,7 @@
 }
 
 #[cfg(procmacro2_unstable)]
-#[cfg(not(feature = "unstable"))]
+#[cfg(not(feature = "nightly"))]
 #[test]
 fn default_span() {
     let start = Span::call_site().start();