function _colGroup(settings) {
		var cols = settings.aoColumns;

		settings.colgroup.empty();

		for (i = 0; i < cols.length; i++) {
			if (cols[i].bVisible) {
				settings.colgroup.append(cols[i].colEl);
			}
		}
	}
Re-insert the `col` elements for current visibility

@param {*} settings DT settings