因为.vue的引入没有后缀名,自己加上
module.exports = { entry: './src/main.js', output: { filename: "./js/bundle.js" }, resolve: { alias: { 'vue$': 'vue/dist/vue.js' // 用 webpack 1 时需用 'vue/dist/vue.common.js' }, extensions: ['*', '.js', '.vue']}}