Add Babel loader to fix tangram.cartodb problem

package.json

@@ -42,6 +42,9 @@
   "devDependencies": {
     "autoprefixer-core": "5.2.1",
     "aws-sdk": "2.0.0-rc11",
+    "babel-core": "6.25.0",
+    "babel-loader": "7.1.1",
+    "babel-preset-es2015": "6.24.1",
     "bluebird": "3.5.0",
     "brfs": "^1.4.3",
     "browserify-resolutions": "1.1.0",

webpack.prod.config.js

@@ -90,6 +90,14 @@ module.exports = env => {
             }
           }
         },
+        {
+          test: /\.js$/,
+          loader: 'babel-loader',
+          include: [resolve(__dirname, 'node_modules/tangram.cartodb')],
+          options: {
+            presets: ['es2015']
+          }
+        },
         {
           test: /\.tpl$/,
           use: 'tpl-loader',