fix(表单设计器): 修复表单设计级联选择动态数据无法获取问题。

ruoyi-ui/public/preview.html

@@ -9,6 +9,7 @@
     <link href="https://lib.baomitu.com/element-ui/2.13.2/theme-chalk/index.css" rel="stylesheet">
     <script src="https://lib.baomitu.com/vue/2.6.11/vue.min.js"></script>
     <script src="https://lib.baomitu.com/vue-router/3.1.3/vue-router.min.js"></script>
+    <script src="https://lib.baomitu.com/axios/0.19.2/axios.min.js"></script>
     <script src="https://lib.baomitu.com/element-ui/2.13.2/index.js"></script>
     <style>
       body{
@@ -34,6 +35,7 @@
     </noscript>
     <div id="previewApp"></div>
     <script type="text/javascript">
+      Vue.prototype.$axios = axios
       const childAttrs = {
         file: '',
         dialog: ' width="600px" class="dialog-width" v-if="visible" :visible.sync="visible" :modal-append-to-body="false" '