C-GETTER: Replace a broken link with a new active one

Author: shamilsan

src/naming.md

@@ -179,7 +179,7 @@ would not be correct to call it `get_path` or `as_path`.
 ### Examples from the standard library
 
 - [`std::io::Cursor::get_mut`](https://doc.rust-lang.org/std/io/struct.Cursor.html#method.get_mut)
-- [`std::ptr::Unique::get_mut`](https://doc.rust-lang.org/std/ptr/struct.Unique.html#method.get_mut)
+- [`std::pin::Pin::get_mut`](https://doc.rust-lang.org/std/pin/struct.Pin.html#method.get_mut)
 - [`std::sync::PoisonError::get_mut`](https://doc.rust-lang.org/std/sync/struct.PoisonError.html#method.get_mut)
 - [`std::sync::atomic::AtomicBool::get_mut`](https://doc.rust-lang.org/std/sync/atomic/struct.AtomicBool.html#method.get_mut)
 - [`std::collections::hash_map::OccupiedEntry::get_mut`](https://doc.rust-lang.org/std/collections/hash_map/struct.OccupiedEntry.html#method.get_mut)