Update Bootstrap to v3.2.0

Bootstrap updated, and to maintain **high quality** of this repository, I've created a pull request to update the files.

One of the updates that will be very useful is the Responsive embeds:

```
<!-- 16:9 aspect ratio -->
<div class="embed-responsive embed-responsive-16by9">
  <iframe class="embed-responsive-item" src="…"></iframe>
</div>

<!-- 4:3 aspect ratio -->
<div class="embed-responsive embed-responsive-4by3">
  <iframe class="embed-responsive-item" src="…"></iframe>
</div>
```

More details: [Bootstrap Responsive Embed](http://getbootstrap.com/components/#responsive-embed).

All information updates can be seen here: [Release v3.2.0](https://github.com/twbs/bootstrap/releases/tag/v3.2.0).