[QUESTION]: lazyload-wrapper class

Hi @ameerthehacker, in the [latest commit](https://github.com/twobin/react-lazyload/commit/fa6cc889131d1ba63cdec440181b5eaf709deb20), you merged a pull request that added this span with the className `lazyload-wrapper`.

Is there a reason for this?

The previous behavior when the children was visible, was not to have any placeholder or wrapper around them.

Now because of this commit, it breaks my layout because of the extra `span` element with that class.

Is this the intended behavior?

Previous code:
```
return this.visible ? this.props.children : this.props.placeholder ? this.props.placeholder : _react2.default.createElement('div', { style: { height: this.props.height }, className: 'lazyload-placeholder' });
```

Now:
```
return _react2.default.createElement(
'span',
{ className: 'lazyload-wrapper', ref: this.setRef },
this.visible ? this.props.children : this.props.placeholder ? this.props.placeholder : _react2.default.createElement('div', {
style: { height: this.props.height },
className: 'lazyload-placeholder'
})
);
```

Please let me know, thanks!