Add prestart command to run the build

Author: weblancaster

package.json

@@ -8,6 +8,7 @@
     "url": "git://github.com/Soundnode/soundnode-app.git"
   },
   "scripts": {
+    "prestart": "npm run webpack:prod && npm run sass:prod",
     "start": "./node_modules/.bin/electron .",
     "build": "npm run clean && npm run webpack:prod && npm run sass:prod && npm run package:all",
     "watch": "npm run webpack:dev & npm run sass:dev",