vendor.css and some js give 404 after build

I created a new project and i've noticed some 404 error after building the demo page:
- `styles/vendor.css`
- `scripts/main.js`
- `scripts/plugins.js`
- `scripts/vendor.js`

bootstrap.css it's inside a build block () but it get merged into main.css so we end with a 404 because `styles/vendor.css` doesn't exist.
`main.js`, `vendor.js` and `plugins.js` also don't get created and provide 404 after build.

Output of `yo --version && echo $PATH $NODE_PATH && node -e 'console.log(process.platform, process.versions)' && cat Gruntfile.js` [here](https://gist.github.com/slackerzz/c0c12bf7d593f62356b1).