build: optimize core-js modules importing

.babelrc

@@ -3,7 +3,11 @@
     [
       "@babel/preset-env",
       {
-        "modules": false
+        "modules": false,
+        "useBuiltIns": "usage",
+        "targets": {
+          "browsers": [">0.25%", "not ie 11", "not op_mini all"]
+        }
       }
     ],
     "@babel/preset-react"

webpack.config.js

@@ -22,7 +22,8 @@ const svgSpriteRule = {
 // ---- entry
 
 const entry = {
-  app: ['whatwg-fetch', '@babel/polyfill', './src/app.js']
+  // app: ['whatwg-fetch', '@babel/polyfill', './src/app.js']
+  app: ['whatwg-fetch', './src/app.js']
 };
 
 // ---- output