fix: 修改moadl定义拖拽，和 绑定style left 与top 值后，点击拖拽飘移的问题

examples/routers/modal.vue

@@ -1,6 +1,12 @@
 <template>
     <div>
         <Button type="primary" @click="modal1 = true">Display dialog box</Button>
+        <Button type="primary" @click="modal2 = true">Display dialog box</Button>
+        <Modal v-model="modal2" draggable title="Common Modal dialog box title"
+               @on-ok="ok"
+               @on-cancel="cancel">
+            <p>2123</p>
+        </Modal>
         <Modal
                 v-model="modal1"
                 title="Common Modal dialog box title"
@@ -52,6 +58,7 @@
         data () {
             return {
                 modal1: false,
+                modal2: false,
                 cityList: [
                     {
                         value: 'New York',