Update 4.2 release notes.

Author: JuanitoFatas

source/4_2_release_notes.md

@@ -85,6 +85,9 @@ Please refer to the [Changelog][railties] for detailed changes.
 *   Introduced `Rails.gem_version` as a convenience method to return `Gem::Version.new(Rails.version)`.
     ([Pull Request](https://github.com/rails/rails/pull/14101))
 
+*   Introduced an `after_bundle` callback in the Rails templates.
+    ([Pull Request](https://github.com/rails/rails/pull/16359))
+
 
 Action Pack
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source/zh-CN/4_2_release_notes.md

@@ -64,6 +64,9 @@ Railties
 * 导入 `Rails.gem_version` 作为返回 `Gem::Version.new(Rails.version)` 的便捷方法。
   ([Pull Request](https://github.com/rails/rails/pull/14101))
 
+* 导入 `after_bundle` 回调至 Rails 模版。
+  ([Pull Request](https://github.com/rails/rails/pull/16359))
+
 Action Pack
 -----------