fix: add decode code result type

demo/camera.html

@@ -20,7 +20,7 @@
     var vConsole = new VConsole();
     console.log('Hello world');
     function main() {
-      var qr = new QrcodeDecoder();
+      var qr = new QrcodeDecoder.default();
       var video = document.querySelector('#video');
       var start = document.querySelector('#start');
       var stop = document.querySelector('#stop');

demo/image.html

@@ -30,7 +30,7 @@
   <script type="module">
     var vConsole = new VConsole();
     function main() {
-      var qr = new QrcodeDecoder();
+      var qr = new QrcodeDecoder.default();
 
       var btn1 = document.querySelector('button#decode1');
       var btn2 = document.querySelector('button#decode2');

demo/video.html

@@ -22,7 +22,7 @@
       var result = document.querySelector('#result');
       var start = document.querySelector('#start');
       var stop = document.querySelector('#stop');
-      var qr = new QrcodeDecoder();
+      var qr = new QrcodeDecoder.default();
 
       start.onclick = startScan;