fix tidy checks

src/libcore/cell.rs

@@ -1165,7 +1165,7 @@ impl<'a, T: ?Sized + fmt::Display> fmt::Display for RefMut<'a, T> {
 /// mutated, and that `&mut T` is unique. When building abstractions like `Cell`, `RefCell`,
 /// `Mutex`, etc, you need to turn these optimizations off. `UnsafeCell` is the only legal way
 /// to do this. When `UnsafeCell<T>` _itself_ is immutably aliased, it is still safe to obtain
-/// a mutable reference to its _interior_ and/or to mutate the interior. However, it is up to 
+/// a mutable reference to its _interior_ and/or to mutate the interior. However, it is up to
 /// the abstraction designer to ensure that no two mutable references obtained this way are active
 /// at the same time, there are no active immutable reference when a mutable reference is obtained
 /// from the cell, and that there are no active mutable references or mutations when an immutable
@@ -1243,7 +1243,7 @@ impl<T: ?Sized> UnsafeCell<T> {
     /// This can be cast to a pointer of any kind.
     /// Ensure that the access is unique (no active references, mutable or not)
     /// when casting to `&mut T`, and ensure that there are no mutations
-	/// or mutable aliases going on when casting to `&T`
+    /// or mutable aliases going on when casting to `&T`
     ///
     /// # Examples
     ///