Another little code question (variable: top)

Hiya!

This line in `lib/simpleslideview.js`: https://github.com/cloudfour/SimpleSlideView/blob/master/lib/simpleslideview.js#L266

Is in the `beforeChangeEnd` callback:

``` javascript
beforeChangeEnd = function() {
if (_this.options.resizeHeight) {
if (_this.options.maintainViewportHeight && window.innerHeight > _this.lastViewportHeight) {
_this.lastViewportHeight = window.innerHeight;
$html.css('min-height', (_this.lastViewportHeight + top) + 'px');
}
return _this.$container.animate({
height: outerHeight($targetView)
}, _this.options.heightDuration, _this.options.easing, onChangeEnd);
} else {
return onChangeEnd();
}
};
```

`top` isn't defined. Not sure what it should be so need a bit of input to fix it!