remove unstable comment

Author: Ariel Ben-Yehuda

src/rt/timer.rs

@@ -75,11 +75,6 @@ pub trait Timer {
     fn sleep_until(&self, deadline: Instant) -> Pin<Box<dyn Sleep>>;
 
     /// Return an `Instant` representing the current time
-    ///
-    /// This function is currently unstable to implement - its
-    /// definition might change in a future version of Hyper
-    ///
-    /// FIXME: do we want to mention this function in the module doc comment?
     fn now(&self) -> Instant {
         Instant::now()
     }