Revert incorrect config change for createStackNavigator docs

Author: levibuzolic

docs/stack-navigator.md

@@ -31,7 +31,7 @@ createStackNavigator({
     // The action and route params are extracted from the path.
 
     // Optional: Override the `navigationOptions` for the screen
-    defaultNavigationOptions: ({ navigation }) => ({
+    navigationOptions: ({ navigation }) => ({
       title: `${navigation.state.params.name}'s Profile'`,
     }),
   },