[Build] use vue-cli to build site (#3734)

build/webpack.doc.js

@@ -1,14 +0,0 @@
-const path = require('path');
-const config = require('./webpack.dev.js');
-
-delete config.serve;
-
-module.exports = Object.assign(config, {
-  mode: 'production',
-  output: {
-    path: path.join(__dirname, '../docs/dist'),
-    publicPath: 'https://youzan.github.io/vant/',
-    filename: '[name].[hash:8].js',
-    chunkFilename: 'async_[name].[chunkhash:8].js'
-  }
-});