fix tests

src/libcore/time.rs

@@ -689,6 +689,7 @@ pub fn div_f32(self, rhs: f32) -> Duration {
     ///
     /// # Examples
     /// ```
+    /// #![feature(div_duration)]
     /// use std::time::Duration;
     ///
     /// let dur1 = Duration::new(2, 700_000_000);
@@ -705,6 +706,7 @@ pub fn div_duration_f64(self, rhs: Duration) -> f64 {
     ///
     /// # Examples
     /// ```
+    /// #![feature(div_duration)]
     /// use std::time::Duration;
     ///
     /// let dur1 = Duration::new(2, 700_000_000);