build(examples): fix webpack-dev-server bug

GUIDE: webpack/webpack-dev-server#2190 (comment)

Author: lbwa

examples/vue.config.js

@@ -1,6 +1,10 @@
 const { resolve } = require('path')
 
 module.exports = {
+  devServer: {
+    // https://github.com/webpack/webpack-dev-server/issues/2190#issuecomment-520670599
+    contentBase: './public'
+  },
   chainWebpack(webpackConf) {
     webpackConf.resolve.alias.set('@src', resolve(__dirname, '../src'))
   }