Add support for WC Variations Radio Buttons

Hi I wanted to make my plugin compatible with Woocommerce Ajax add to cart for variable products, but I realized I would have to make some changes in this plugin js.

We would get compatibility by replacing line 20 with this:

variations = $variation_form.find( 'select[name^=attribute]' );

if ( ! variations.length) {
	variations = $variation_form.find( 'input[name^=attribute]:checked' );
}

Maybe this can be included in the next version

https://wordpress.org/plugins/woocommerce-ajax-add-to-cart-for-variable-products/