Bug with ExpandRow if I have another expand row tables inside

[kosuha606]

Hello, if we have expand row in table and inside this expand row also have expand row table and inner tables have disabled property on expand button, then top expand button what doesn't have disabled not work.

I think what it can be fixed here
https://github.com/kartik-v/yii2-grid/blob/master/src/assets/js/kv-grid-expand.js#L118

$icon = $el.find('.kv-expand-icon')
replace to 
$icon = $el.find('>.kv-expand-icon')

PS. Such table works fine in release 3.0