Revert "Use node6 es2015 features; remove extra transforms (#327)"

This reverts commit 9e3fe9228d.

@freebroccolo while great in theory, this breaks uglifyjs.
minification provides an important advantage in interpretation
time (and therefore reduced bootup time)

app/package.json

@@ -27,6 +27,7 @@
     "babel-core": "6.10.4",
     "babel-eslint": "6.1.2",
     "babel-loader": "6.2.4",
+    "babel-preset-es2015-native-modules": "6.9.0",
     "babel-preset-react": "6.11.1",
     "eslint": "3.1.1",
     "eslint-config-standard": "5.3.5",
@@ -66,6 +67,7 @@
   },
   "babel": {
     "presets": [
+      "es2015-native-modules",
       "react"
     ]
   },

index.js

@@ -8,9 +8,6 @@ const isDev = require('electron-is-dev');
 const AutoUpdater = require('./auto-updater');
 const toHex = require('convert-css-color-name-to-hex');
 
-// --harmony enables a few remaining es2015 features not defaulted in node 6
-app.commandLine.appendSwitch('js-flags', '--harmony');
-
 // set up config
 const config = require('./config');
 config.init();