libcore/Result - Change expect feature flag to result_expect

Author: thepowersgang

src/libcore/result.rs

@@ -741,7 +741,7 @@ impl<T, E: fmt::Debug> Result<T, E> {
     /// x.expect("Testing expect"); // panics with `Testing expect: emergency failure`
     /// ```
     #[inline]
-    #[unstable(feature = "core", reason = "newly introduced")]
+    #[unstable(feature = "result_expece", reason = "newly introduced")]
     pub fn expect(self, msg: &str) -> T {
         match self {
             Ok(t) => t,