add dangerouslyGetParent() to flow typings (#5014)

* add dangerouslyGetParent() to flow typings

* Update CHANGELOG.md

packages/react-navigation/CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+- added `dangerouslyGetParent()` to flow typings
+
 ## [2.16.0] - [2018-09-19](https://github.com/react-navigation/react-navigation/releases/tag/2.16.0)
 
 ### Changed

packages/react-navigation/flow/react-navigation.js

@@ -528,6 +528,7 @@ declare module 'react-navigation' {
       callback: NavigationEventCallback
     ) => NavigationEventSubscription,
     getParam: (paramName: string, fallback?: any) => any,
+    dangerouslyGetParent: () => NavigationScreenProp<*>,
     isFocused: () => boolean,
     // Shared action creators that exist for all routers
     goBack: (routeKey?: ?string) => boolean,