Output only the necessary vendor prefixes

- Firefox supports both animations and transforms since version 15 with the standard notation, so no need for `-moz` vendor prefixes

## Before
Using CSS3 mixins with both transforms and animations leads to this kind of nonsense:

```css
@-webkit-keyframes pulse {
  0% {
    opacity: 1;
    -webkit-transform: scale(1);
    -moz-transform: scale(1);
    -ms-transform: scale(1);
    -o-transform: scale(1);
    transform: scale(1);
  }

  100% {
    opacity: 0;
    -webkit-transform: scale(2);
    -moz-transform: scale(2);
    -ms-transform: scale(2);
    -o-transform: scale(2);
    transform: scale(2);
  }
}
@-moz-keyframes pulse {
  0% {
    opacity: 1;
    -webkit-transform: scale(1);
    -moz-transform: scale(1);
    -ms-transform: scale(1);
    -o-transform: scale(1);
    transform: scale(1);
  }

  100% {
    opacity: 0;
    -webkit-transform: scale(2);
    -moz-transform: scale(2);
    -ms-transform: scale(2);
    -o-transform: scale(2);
    transform: scale(2);
  }
}
@keyframes pulse {
  0% {
    opacity: 1;
    -webkit-transform: scale(1);
    -moz-transform: scale(1);
    -ms-transform: scale(1);
    -o-transform: scale(1);
    transform: scale(1);
  }

  100% {
    opacity: 0;
    -webkit-transform: scale(2);
    -moz-transform: scale(2);
    -ms-transform: scale(2);
    -o-transform: scale(2);
    transform: scale(2);
  }
}
```

## After

```css
@-webkit-keyframes pulse {
    0% {
        opacity: 1;
        -webkit-transform: scale(1);
        transform: scale(1);
    }

    100% {
        opacity: 0;
        -webkit-transform: scale(2);
        transform: scale(2);
    }
}
@keyframes pulse {
    0% {
        opacity: 1;
        transform: scale(1);
    }

    100% {
        opacity: 0;
        transform: scale(2);
    }
}
```


![ ](http://gifs.joelglovier.com/no/dikembe-mutumbo-nope.gif)