fix buttonText is null in LoginItem

package.json

@@ -24,6 +24,7 @@
   },
   "dependencies": {
     "@antv/data-set": "^0.9.0",
+    "@babel/polyfill": "^7.0.0",
     "@babel/runtime": "^7.0.0",
     "antd": "^3.9.0",
     "bizcharts": "^3.1.10",

src/components/Login/LoginItem.js

@@ -8,6 +8,10 @@ import LoginContext from './loginContext';
 const FormItem = Form.Item;
 
 class WarpFormItem extends Component {
+  static defaultProps = {
+    buttonText: '获取验证码',
+  };
+
   constructor(props) {
     super(props);
     this.state = {

src/global.js

+import '@babel/polyfill';