Add breaking change reference

Author: dplewis

CHANGELOG.md

@@ -7,7 +7,7 @@
 [Full Changelog](https://github.com/parse-community/Parse-SDK-JS/compare/2.19.0...3.0.0)
 
 **Breaking Changes**
-For security purposes, logIn will default to `POST` instead of `GET` method.
+For security purposes, logIn will default to `POST` instead of `GET` method. ([#1284](https://github.com/parse-community/Parse-SDK-JS/pull/1284))
 If you need to use `GET` set the `usePost` option to false.
 `Parse.User.logIn('username', 'password', { usePost: false })`