PanelBody.toggle() should update setState

[BE-Webdesign]

Current:

toggle( event ) {
	event.preventDefault();
	this.setState( {
		opened: ! this.state.opened,
	} );
}

Should be:

toggle( event ) {
	event.preventDefault();
	this.setState( ( previousState ) => ( {
		opened: ! previousState.opened,
	} ) );
}