fix: exportPNG not display image markup (#4672)

Co-authored-by: heshenglei <[email protected]>

Author: q32757468

packages/x6-plugin-export/src/index.ts

@@ -1,14 +1,14 @@
 import {
+  Basecoat,
   DataUri,
-  NumberExt,
+  Dom,
   FunctionExt,
-  Vector,
+  Graph,
+  KeyValue,
+  NumberExt,
   Rectangle,
   Size,
-  KeyValue,
-  Basecoat,
-  Dom,
-  Graph,
+  Vector,
 } from '@antv/x6'
 import './api'
 
@@ -213,6 +213,7 @@ export class Export extends Basecoat<Export.EventArgs> implements Graph.Plugin {
           DataUri.imageToDataUri(url, (err, dataUri) => {
             if (!err && dataUri) {
               vImage.attr('xlink:href', dataUri)
+              vImage.attr('href', dataUri)
             }
             resolve()
           })