Update ObjectIdentifier.swift

Author: sunbohong

stdlib/public/core/ObjectIdentifier.swift

@@ -14,14 +14,15 @@
 ///
 /// In Swift, only class instances and metatypes have unique identities. There
 /// is no notion of identity for structs, enums, functions, or tuples.
+///
 /// `ObjectIdentifier` is only guaranteed to remain unique for the
 /// lifetime of an object. When the instance gets deallocated, its object 
 /// identifier may be reused for a different object. (Internally, objects are
 /// identified by their memory location.)
+///
 /// If you need an object identifier over the lifetime of an object, it may
 /// be appropriate to provide a custom implementation of `Identifiable`.
 @frozen // trivial-implementation
-/// 
 public struct ObjectIdentifier {
   @usableFromInline // trivial-implementation
   internal let _value: Builtin.RawPointer