update virtual scroll unit test

Author: huangshuwei

tests/unit/specs/__snapshots__/ve-table-virtual-scroll.spec.js.snap

@@ -3,7 +3,9 @@
 exports[`veTable virtual scroll render same row height 1`] = `
 <div class="ve-table">
   <div class="ve-table-container ve-table-border-around ve-table-virtual-scroll" style="max-height: 500px; height: 500px;">
-    <div class="ve-table-virtual-phantom"></div>
+    <div class="ve-table-virtual-phantom">
+      <div style="width: 100%;"></div>
+    </div>
     <table class="ve-table-content ve-table-border-x">
       <colgroup>
         <col style="width: 200px;">

tests/unit/specs/ve-table-virtual-scroll.spec.js

@@ -396,7 +396,7 @@ describe("veTable virtual scroll", () => {
 
         await later();
 
-        expect(wrapper.find(".ve-table-expand-tr").exists()).toBe(true);
+        expect(wrapper.find(".ve-table-row-expand-icon").exists()).toBe(true);
 
         // default buffer=1
         expect(wrapper.findAll(".ve-table-body-tr").length).toBeGreaterThan(