fix: add webpack-preprocessor, fixes babel 7 compatibility issues

closes #2538
closes #2465

Author: haoqunjiang

packages/@vue/cli-plugin-e2e-cypress/generator/template/tests/e2e/plugins/index.js

@@ -1,6 +1,12 @@
 // https://docs.cypress.io/guides/guides/plugins-guide.html
+const webpack = require('@cypress/webpack-preprocessor')
 
 module.exports = (on, config) => {
+  on('file:preprocessor', webpack({
+    webpackOptions: require('@vue/cli-service/webpack.config'),
+    watchOptions: {},
+  }))
+
   return Object.assign({}, config, {
     fixturesFolder: 'tests/e2e/fixtures',
     integrationFolder: 'tests/e2e/specs',

packages/@vue/cli-plugin-e2e-cypress/package.json

@@ -22,6 +22,7 @@
     "access": "public"
   },
   "dependencies": {
+    "@cypress/webpack-preprocessor": "^3.0.0",
     "@vue/cli-shared-utils": "^3.0.2",
     "cypress": "^3.0.2",
     "eslint-plugin-cypress": "^2.0.1"