floatHeaderOptions 'scrollingTop' should be 'top'

[arkurth]

This is a minor suggestion to update README.md and your docs.

floaThead no longer uses the scrollingTop option. It was renamed to top in version 1.3.1 and support for the parameter was removed at some point.

Specifying scrollingTop no longer has any effect on the placement of the header:

echo GridView::widget([
    'floatHeader'=>true,
    'floatHeaderOptions'=>[
        'scrollingTop'=>'100',
        'debug'=>true,
    ],
    ...
]);

The following appears in console.log with floaThead's debug option enabled:

jquery.floatThead.min.js:1 jQuery.floatThead: Used [scrollingTop] key to init plugin, but that param is not an option for the plugin. Valid options are: headerCellSelector, zIndex, position, top, bottom, scrollContainer, responsiveContainer, getSizingRow, floatTableClass, floatWrapperClass, floatContainerClass, copyTableClass, autoReflow, debug, support, floatContainerCss

Specifying top does cause the header to be positioned as intended:

echo GridView::widget([
    'floatHeader'=>true,
    'floatHeaderOptions'=>[
        'top'=>'100',
    ],
    ...
]);

Thanks for all your great work!