remove babel-polyfill, add core-js

package.json

@@ -20,15 +20,13 @@
   },
   "browserslist": [
     "> 1%",
-    "last 2 versions",
-    "ie >= 9"
+    "last 2 versions"
   ],
   "devDependencies": {
     "@babel/core": "^7.4.5",
     "@babel/node": "^7.4.5",
     "@babel/plugin-syntax-dynamic-import": "^7.2.0",
     "@babel/plugin-transform-runtime": "^7.4.4",
-    "@babel/polyfill": "^7.4.4",
     "@babel/preset-env": "^7.4.5",
     "@babel/preset-stage-2": "^7.0.0",
     "@babel/runtime": "^7.4.5",
@@ -41,6 +39,7 @@
     "browser-sync": "^2.26.7",
     "connect-history-api-fallback": "^1.6.0",
     "copy-webpack-plugin": "^5.0.3",
+    "core-js": "^3.1.3",
     "css-loader": "^3.0.0",
     "dart-sass": "^1.21.0",
     "eslint": "^5.16.0",