Update webpacker (babel7)

.babelrc

@@ -1,9 +1,10 @@
 {
   "presets": [
-    ["env", {
+    [
+      "@babel/env",
+      {
         "modules": false,
         "targets": {
-        // See config/browser.rb
           "browsers": [
             "> 1%",
             "Chrome >= 50",
@@ -16,13 +17,38 @@
           ],
           "uglify": true
         },
-      "useBuiltIns": true
-    }]
+        "forceAllTransforms": true,
+        "useBuiltIns": "entry"
+      }
+    ]
   ],
-
   "plugins": [
-    "syntax-dynamic-import",
-    "transform-object-rest-spread",
-    ["transform-class-properties", { "spec": true }]
+    "@babel/plugin-transform-destructuring",
+    "@babel/plugin-syntax-dynamic-import",
+    [
+      "@babel/plugin-proposal-object-rest-spread",
+      {
+        "useBuiltIns": true
+      }
+    ],
+    [
+      "@babel/plugin-transform-runtime",
+      {
+        "helpers": false,
+        "regenerator": true
+      }
+    ],
+    [
+      "@babel/plugin-transform-regenerator",
+      {
+        "async": false
+      }
+    ],
+    [
+      "@babel/plugin-proposal-class-properties",
+      {
+        "loose": true
+      }
+    ]
   ]
 }

app/javascript/packs/mailjet.js

@@ -1,7 +1,7 @@
 // Include runtime-polyfills for older browsers.
 // Due to .babelrc's 'useBuiltIns', only polyfills actually
 // required by the browsers we support will be included.
-import 'babel-polyfill';
+import '@babel/polyfill';
 
 // This file is copied from mailjet. We serve here a copy of it ourselves
 // to avoid loading javascript files from other domains on the frontpage.

app/javascript/shared/polyfills.js

@@ -1,5 +1,5 @@
 // Include runtime-polyfills for older browsers.
 // Due to .babelrc's 'useBuiltIns', only polyfills actually
 // required by the browsers we support will be included.
-import 'babel-polyfill';
+import '@babel/polyfill';
 import 'dom4';

package.json

@@ -1,6 +1,6 @@
 {
   "dependencies": {
-    "@rails/webpacker": "4.0.0-pre.2",
+    "@rails/webpacker": "4.0.0-pre.3",
     "@sentry/browser": "^4.0.4",
     "@turf/area": "^6.0.1",
     "activestorage": "^5.2.1",
@@ -19,10 +19,10 @@
   },
   "devDependencies": {
     "eclint": "^2.8.0",
-    "eslint": "^5.6.0",
-    "eslint-config-prettier": "^3.1.0",
-    "eslint-plugin-prettier": "^2.6.2",
-    "prettier": "^1.14.3",
+    "eslint": "^5.9.0",
+    "eslint-config-prettier": "^3.3.0",
+    "eslint-plugin-prettier": "^3.0.0",
+    "prettier": "^1.15.3",
     "webpack-dev-server": "^3.1.9"
   },
   "scripts": {