twbs/bootstrap — pull request #13760 by dkrnl (2014-06-09 06:07:32+00:00)
Title: Add responsive media-mixins shortcut

usage example:
```less
.media-xs({
div {
border:1px solid red;
}
})
```
result:
```css
@media (max-width: 767px) {
div {
border:1px solid red;
}
}
```