How to add gradient color in AppBar in Flutter

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: Scaffold(
        appBar: AppBar(
          title: Text('Flutter Demo'),

          flexibleSpace: Container(
            decoration: BoxDecoration(
              gradient: LinearGradient(
                begin: Alignment.centerLeft,
                end: Alignment.centerRight,
                colors: <Color>[
                  Colors.red,
                  Colors.blue
                ],
              ),
            ),
          ),

        ),
      ),
    );
  }
}