updated new flutter version

lib/widgets/general/download_item.dart

@@ -2,6 +2,7 @@
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:url_launcher/url_launcher.dart';
+import "package:universal_html/html.dart";
 
 import '../../constants.dart';
 import '../../generated/l10n.dart';
@@ -22,7 +23,7 @@ class DownloadItem extends StatefulWidget {
 }
 
 class DownloadItemState extends State<DownloadItem> {
-  final double buttonWidth = 114.0;
+  final double buttonWidth = 122.0;
   final double iconWidth = 48.0;
 
   @override
@@ -275,8 +276,14 @@ class DownloadItemState extends State<DownloadItem> {
           ],
         ),
         onPressed: () async {
-          if (await canLaunch(downloadUrl)) {
-            await launch('$downloadUrl');
+          if (kIsWeb) {
+            AnchorElement anchorElement = new AnchorElement(href: downloadUrl);
+            anchorElement.download = downloadUrl;
+            anchorElement.click();
+          } else {
+            if (!await launchUrl(Uri.parse('$downloadUrl'))) {
+              throw 'Could not launch $downloadUrl';
+            }
           }
         },
       );