update release notes wrt #438

Author: cowtowncoder

release-notes/CREDITS-2.x

@@ -90,3 +90,7 @@ Drew Stephens (dinomite@github)
 * Contributed fix for #281: KotlinObjectSingletonDeserializer fails to deserialize
     previously serialized JSON as it doesn't delegate deserializeWithType
   (2.11.0)
+
+Kiyori Miyata aka "wrongwrong" (k163377@github)
+* Contributed #438: Fixed mapping failure when `private` `companion object` is named
+ (2.13.0)

release-notes/VERSION-2.x

@@ -16,7 +16,8 @@ Co-maintainers:
 
 2.13.0 (not yet released)
 
-No changes since 2.12
+#438: Fixed mapping failure when `private` `companion object` is named
+ (reported, fix contributed by k163377@github)
 
 2.12.3 (12-Apr-2021)