Upgrade follow latest

example/lib/main.dart

@@ -1,20 +1,21 @@
 import 'package:country_code_picker/country_code_picker.dart';
-import 'package:country_code_picker/country_localizations.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_localizations/flutter_localizations.dart';
 
-void main() => runApp(MyApp());
+void main() => runApp(const MyApp());
 
 class MyApp extends StatefulWidget {
+  const MyApp({Key key}) : super(key: key);
+
   @override
-  _MyAppState createState() => new _MyAppState();
+  MyAppState createState() => MyAppState();
 }
 
-class _MyAppState extends State<MyApp> {
+class MyAppState extends State<MyApp> {
   @override
   Widget build(BuildContext context) {
-    return new MaterialApp(
-      supportedLocales: [
+    return MaterialApp(
+      supportedLocales: const [
         Locale("af"),
         Locale("am"),
         Locale("ar"),
@@ -86,13 +87,13 @@ class _MyAppState extends State<MyApp> {
         Locale("vi"),
         Locale("zh")
       ],
-      localizationsDelegates: [
+      localizationsDelegates: const [
         CountryLocalizations.delegate,
         GlobalMaterialLocalizations.delegate,
         GlobalWidgetsLocalizations.delegate,
       ],
-      home: new Scaffold(
-        appBar: new AppBar(
+      home: Scaffold(
+        appBar: AppBar(
           title: const Text('CountryPicker Example'),
         ),
         body: Center(
@@ -103,26 +104,26 @@ class _MyAppState extends State<MyApp> {
                 onChanged: print,
                 // Initial selection and favorite can be one of code ('IT') OR dial_code('+39')
                 initialSelection: 'IT',
-                favorite: ['+39', 'FR'],
-                countryFilter: ['IT', 'FR'],
+                favorite: const ['+39', 'FR'],
+                countryFilter: const ['IT', 'FR'],
                 showFlagDialog: false,
                 comparator: (a, b) => b.name.compareTo(a.name),
                 //Get the country information relevant to the initial selection
-                onInit: (code) =>
-                    print("on init ${code.name} ${code.dialCode} ${code.name}"),
+                onInit: (code) => debugPrint(
+                    "on init ${code.name} ${code.dialCode} ${code.name}"),
               ),
               CountryCodePicker(
                 onChanged: print,
                 // Initial selection and favorite can be one of code ('IT') OR dial_code('+39')
                 initialSelection: 'IT',
-                favorite: ['+39', 'FR'],
-                countryFilter: ['IT', 'FR'],
+                favorite: const ['+39', 'FR'],
+                countryFilter: const ['IT', 'FR'],
                 // flag can be styled with BoxDecoration's `borderRadius` and `shape` fields
                 flagDecoration: BoxDecoration(
                   borderRadius: BorderRadius.circular(7),
                 ),
               ),
-              SizedBox(
+              const SizedBox(
                 width: 400,
                 height: 60,
                 child: CountryCodePicker(
@@ -141,11 +142,11 @@ class _MyAppState extends State<MyApp> {
                 width: 400,
                 height: 60,
                 child: CountryCodePicker(
-                  onChanged: (e) => print(e.toLongString()),
+                  onChanged: (element) => debugPrint(element.toLongString()),
                   initialSelection: 'TF',
                   showCountryOnly: true,
                   showOnlyCountryWhenClosed: true,
-                  favorite: ['+39', 'FR'],
+                  favorite: const ['+39', 'FR'],
                 ),
               ),
               SizedBox(
@@ -157,7 +158,7 @@ class _MyAppState extends State<MyApp> {
                   initialSelection: 'TF',
                   showCountryOnly: true,
                   showOnlyCountryWhenClosed: true,
-                  favorite: ['+39', 'FR'],
+                  favorite: const ['+39', 'FR'],
                 ),
               ),
             ],