Update NavigatorIOS.ios.js

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Closes https://github.com/facebook/react-native/pull/8982

Differential Revision: D3612982

fbshipit-source-id: 2996730e51ae7a243697f305cd2ed2eb0d2985a8

Libraries/Components/Navigation/NavigatorIOS.ios.js

@@ -100,7 +100,7 @@ type Event = Object;
  * animations and behavior from UIKIt.
  *
  * As the name implies, it is only available on iOS. Take a look at
- * [`Navigator`](/docs/navigator.html) for a similar solution for your
+ * [`Navigator`](/react-native/docs/navigator.html) for a similar solution for your
  * cross-platform needs, or check out
  * [react-native-navigation](https://github.com/wix/react-native-navigation), a
  * component that aims to provide native navigation on both iOS and Android.