fixed deprecated babel-preset-es2015 dependency

Author: Yevhen Kochuh

package.json

@@ -10,7 +10,7 @@
   "devDependencies": {
     "babel-core": "latest",
     "babel-loader": "^6.2.8",
-    "babel-preset-es2015": "^6.18.0",
+    "babel-preset-env": "latest",
     "copy-webpack-plugin": "^4.0.1",
     "cross-env": "^5.0.1",
     "css-loader": "^0.26.1",

webpack.config.js

@@ -25,7 +25,7 @@ const config = {
         exclude: /node_modules/,
         use: [{
           loader: 'babel-loader',
-          options: { presets: ['es2015'] }
+          options: { presets: ['env'] }
         }]
       },
       {