fixed typo in "linking" docs

Summary:
Fixing a typo found via https://facebook.github.io/react-native/docs/linking.html

n/a (they're docs)
Closes https://github.com/facebook/react-native/pull/13440

Differential Revision: D4875315

Pulled By: javache

fbshipit-source-id: 919cf263dba5fb3e8eda6b5181b7b88e1698ef6f

Libraries/Linking/Linking.js

@@ -58,7 +58,7 @@ const LinkingManager = Platform.OS === 'android' ?
  * NOTE: On iOS you'll need to link `RCTLinking` to your project by following
  * the steps described [here](docs/linking-libraries-ios.html#manual-linking).
  * In case you also want to listen to incoming app links during your app's
- * execution you'll need to add the following lines to you `*AppDelegate.m`:
+ * execution you'll need to add the following lines to your `*AppDelegate.m`:
  *
  * ```
  * #import <React/RCTLinkingManager.h>