fix(waterfall): should compile to es5

packages/vant-waterfall/babel.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  presets: ['@babel/env'],
+};

packages/vant-waterfall/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@vant/waterfall",
-  "version": "1.0.1",
+  "version": "1.0.2",
   "description": "vant waterfall component",
   "main": "lib/index.js",
   "publishConfig": {
@@ -13,9 +13,8 @@
   "license": "MIT",
   "repository": "https://github.com/youzan/vant/tree/dev/packages/vant-waterfall",
   "devDependencies": {
-    "@babel/cli": "^7.4.4",
-    "@babel/core": "^7.4.4",
-    "@babel/plugin-transform-object-assign": "^7.2.0",
-    "@babel/preset-env": "^7.4.4"
+    "@babel/cli": "^7.8.4",
+    "@babel/core": "^7.9.0",
+    "@babel/preset-env": "^7.9.5"
   }
 }