refactor: mark initial state as stale to determine when to rehydrate (#23)

example/StackNavigator.tsx

@@ -86,9 +86,10 @@ const StackRouter: Router<CommonAction | Action> = {
   getRehydratedState({ routeNames, partialState }) {
     let state = partialState;
 
-    if (state.routeNames === undefined || state.key === undefined) {
+    if (state.stale) {
       state = {
         ...state,
+        stale: false,
         routeNames,
         key: `stack-${shortid()}`,
       };

example/TabNavigator.tsx

@@ -72,9 +72,10 @@ const TabRouter: Router<Action | CommonAction> = {
   getRehydratedState({ routeNames, partialState }) {
     let state = partialState;
 
-    if (state.routeNames === undefined || state.key === undefined) {
+    if (state.stale) {
       state = {
         ...state,
+        stale: false,
         routeNames,
         key: `tab-${shortid()}`,
       };

example/index.tsx

@@ -3,9 +3,9 @@ import { render } from 'react-dom';
 import {
   NavigationContainer,
   CompositeNavigationProp,
-  PartialState,
   NavigationProp,
   RouteProp,
+  InitialState,
 } from '../src';
 import StackNavigator, { StackNavigationProp } from './StackNavigator';
 import TabNavigator, { TabNavigationProp } from './TabNavigator';
@@ -143,7 +143,7 @@ const Fifth = ({
 
 const PERSISTENCE_KEY = 'NAVIGATION_STATE';
 
-let initialState: PartialState | undefined;
+let initialState: InitialState | undefined;
 
 try {
   initialState = JSON.parse(localStorage.getItem(PERSISTENCE_KEY) || '');