Updating the native code to make it match reality.

Summary:
In the native code, you must use RCTLinkingManager instead of LinkingManager and you have to import it as well.
Closes https://github.com/facebook/react-native/pull/5830

Reviewed By: svcscm

Differential Revision: D2921718

Pulled By: androidtrunkagent

fb-gh-sync-id: a95ec358c69e8830b7f0fb2ec60baefc06139758
shipit-source-id: a95ec358c69e8830b7f0fb2ec60baefc06139758

Libraries/Linking/Linking.js

@@ -53,10 +53,12 @@ const DEVICE_NOTIF_EVENT = 'openURL';
  * execution you'll need to add the following lines to you `*AppDelegate.m`:
  *
  * ```
+ *#import "RCTLinkingManager.h" 
+ *
  * - (BOOL)application:(UIApplication *)application openURL:(NSURL *)url
  *   sourceApplication:(NSString *)sourceApplication annotation:(id)annotation
  * {
- *   return [LinkingManager application:application openURL:url
+ *   return [RCTLinkingManager application:application openURL:url
  *                       sourceApplication:sourceApplication annotation:annotation];
  * }
  *
@@ -64,7 +66,7 @@ const DEVICE_NOTIF_EVENT = 'openURL';
  * - (BOOL)application:(UIApplication *)application continueUserActivity:(NSUserActivity *)userActivity
  *  restorationHandler:(void (^)(NSArray * _Nullable))restorationHandler
  * {
- *  return [LinkingManager application:application
+ *  return [RCTLinkingManager application:application
  *                   continueUserActivity:userActivity
  *                     restorationHandler:restorationHandler];
  * }