Fix link

Author: satya164

versioned_docs/version-4.x/custom-navigators.md

@@ -4,7 +4,7 @@ title: Custom navigators
 sidebar_label: Custom navigators
 ---
 
-A navigator is any React component that has a [router](https://github.com/react-navigation/react-navigation-core/blob/master/src/routers/StackRouter.js) on it, to define the navigation behavior. Each navigator is given a `navigation` prop, which allows the parent to control the navigation state.
+A navigator is any React component that has a [router](https://github.com/react-navigation/react-navigation/tree/4.x/packages/core/src/routers/StackRouter.js) on it, to define the navigation behavior. Each navigator is given a `navigation` prop, which allows the parent to control the navigation state.
 
 ## Extending Navigators