Adjust doc comment of Condvar::wait_while

The existing phrasing implies that a notification must be received for `wait_while` to return. The phrasing is changed to make no such implication.

library/std/src/sync/condvar.rs

@@ -195,8 +195,10 @@ impl Condvar {
         if poisoned { Err(PoisonError::new(guard)) } else { Ok(guard) }
     }
 
-    /// Blocks the current thread until this condition variable receives a
-    /// notification and the provided condition is false.
+    /// Blocks the current thread until the provided `condition` is met.
+    ///
+    /// While `condition` is not met, this function will [`wait`] for
+    /// notification, before again checking `condition`.
     ///
     /// This function will atomically unlock the mutex specified (represented by
     /// `guard`) and block the current thread. This means that any calls