RefreshIndicator is broken

main.dart

import 'package:flutter/material.dart';

main() {
  runApp(
    MaterialApp(
      home: Scaffold(
        body: RefreshIndicator(
          onRefresh: () async => Future.delayed(Duration(seconds: 1)),
          child: ListView.builder(
            itemBuilder: (context, index) => ListTile(
              title: Text('$index'),
            ),
            itemCount: 19,
          ),
        ),
      ),
    ),
  );
}