Add warning about invalid token

app/index.js

@@ -7,13 +7,14 @@ import BusyIndicator from 'react-native-busy-indicator';
 import token from './api/token';
 import { checkToken } from './api/CircleCI';
 
-require('moment-duration-format');
+import 'moment-duration-format';
 
 const {
   Navigator,
   StyleSheet,
   Platform,
-  View
+  View,
+  Alert
 } = React;
 
 const styles = StyleSheet.create({
@@ -28,6 +29,10 @@ const styles = StyleSheet.create({
   }
 });
 
+const LOGGED_IN_ROUTE = RouteMaster.get('HOME');
+const LOGIN_ROUTE = RouteMaster.get('LOGIN');
+
+
 export default class App extends React.Component {
   constructor() {
     super();
@@ -49,18 +54,31 @@ export default class App extends React.Component {
     );
   }
 
+  warnInvalidToken() {
+    Alert.alert(
+      'Token Invalidated',
+      'The token you used previously is now invalid. Please generate a new one in your account settings.',
+      [
+        { text: 'ok' }
+      ]
+    );
+  }
+
   componentWillMount() {
     token.get().then(function (CIToken) {
       if (!CIToken) {
         this.setState({
-          initialRoute: RouteMaster.get('HOME')
+          initialRoute: LOGIN_ROUTE
         });
         return;
       }
       checkToken(CIToken).then(function (isValid) {
         this.setState({
-          initialRoute: isValid ? RouteMaster.get('HOME') : RouteMaster.get('LOGIN')
+          initialRoute: isValid ? LOGGED_IN_ROUTE : LOGIN_ROUTE
         });
+        if (!isValid) {
+          this.warnInvalidToken();
+        }
       }.bind(this));
     }.bind(this));
   }