fix link to PinMut

Author: nivkner

src/libcore/marker.rs

@@ -630,8 +630,8 @@ unsafe impl<'a, T: ?Sized> Freeze for &'a mut T {}
 ///
 /// This trait is automatically implemented for almost every type.
 ///
-/// [`PinMut`]: ../mem/struct.PinMut.html
 /// [`replace`]: ../mem/fn.replace.html
+/// [`PinMut`]: ../pin/struct.PinMut.html
 #[unstable(feature = "pin", issue = "49150")]
 pub auto trait Unpin {}