Fix slice::binary_search_by_key doc tests

Author: circuitfox

src/libcollections/slice.rs

@@ -1116,10 +1116,10 @@ impl<T> [T] {
     ///          (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
     ///          (1, 21), (2, 34), (4, 55)];
     ///
-    /// assert_eq!(s.binary_search_by_key(&13, |&(a,b)| b),  Ok(9));
-    /// assert_eq!(s.binary_search_by_key(&4, |&(a,b)| b),   Err(7));
-    /// assert_eq!(s.binary_search_by_key(&100, |&(a,b)| b), Err(13));
-    /// let r = s.binary_search_by_key(&1, |&(a,b)| b);
+    /// assert_eq!(s.binary_search_by_key(&13, |&(a, ref b)| b),  Ok(9));
+    /// assert_eq!(s.binary_search_by_key(&4, |&(a, ref b)| b),   Err(7));
+    /// assert_eq!(s.binary_search_by_key(&100, |&(a, ref b)| b), Err(13));
+    /// let r = s.binary_search_by_key(&1, |&(a, ref b)| b);
     /// assert!(match r { Ok(1...4) => true, _ => false, });
     /// ```
     #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]