desnot work on my ios device


## System info

Issue occurs on: iOS
Plugin version: flutter_webview_plugin: any
Flutter doctor output:

```
flutter: 0.1
flutter: ┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
flutter: │ #0 showLog (package:union_flutter/appkit/util/util.dart:1:1207)
flutter: │ #1 _WebViewPageState.initState.() (package:union_flutter/module/web_page/web_view_page.dart:33:7)
flutter: ├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄
flutter: │ 🐛 onUrlChangeed https://pages.yiwuhaoyun.com/rent
flutter: └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
flutter: ┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
flutter: │ #0 showLog (package:union_flutter/appkit/util/util.dart:1:1207)
flutter: │ #1 _WebViewPageState.initState.() (package:union_flutter/module/web_page/web_view_page.dart:33:7)
flutter: ├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄
flutter: │ 🐛 onUrlChangeed http://pages.yiwuhaoyun.com/rent/

## Steps to Reproduce
here is my code

import 'dart:core';

import 'package:flutter/material.dart';
import 'package:flutter_webview_plugin/flutter_webview_plugin.dart';
import 'package:union_flutter/appkit/util/util.dart';

class WebViewPage extends StatefulWidget {
final String url;
final String title;
static const String routeName = "/webview";

WebViewPage({this.url, this.title});

_WebViewPageState createState() => _WebViewPageState();
}

class _WebViewPageState extends State {
final flutterWebviewPlugin = new FlutterWebviewPlugin();

final GlobalKey _scaffoldKey = GlobalKey();
var lineProgress;

@override
void initState() {
super.initState();
//showLog('WebViewPage ${Uri.encodeFull(widget.url)}');
flutterWebviewPlugin.onUrlChanged.listen((String url) {
showLog('onUrlChangeed '+url);
});
flutterWebviewPlugin.onProgressChanged.listen((progress) {
print(progress);
setState(() {
lineProgress = progress;
});
});
}

_progressBar(double progress, BuildContext context) {
return LinearProgressIndicator(
backgroundColor: Colors.white70.withOpacity(0),
value: progress == 1.0 ? 0 : progress,
valueColor: new AlwaysStoppedAnimation(Colors.white),
);
}

@override
Widget build(BuildContext context) {
return WebviewScaffold(
appBar: AppBar(
title: Text(widget.title),
bottom: PreferredSize(
child: _progressBar(lineProgress, context),
preferredSize: Size.fromHeight(3.0),
),
),
key: ObjectKey(widget.url),
url: Uri.encodeFull(widget.url),
withZoom: true,
withLocalStorage: true,
withJavascript: true,
useWideViewPort: true,
displayZoomControls: true,
withOverviewMode: true,
);
}

@override
void dispose() {
super.dispose();
}
}

1.the onUrlChange was called twice.and change my url from “https” to "http"
2.I add it in my homepage _pages.add(WebViewPage(
url: URLS.RENT_URL,
title: '租买货车',
));
3. ...

## Logs

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```

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```