Default lightbox quantity to 1

gistfile1.txt

<?php
// Add following to your theme's functions.php file or use something like https://wordpress.org/plugins/custom-css-js-php/
add_action( 'sunshine_before_add_to_cart_form', 'sunshine_lightbox_default_qty_1' );
function sunshine_lightbox_default_qty_1() {
?>
	<script>
	jQuery( document ).ready( function($){
		$( 'input[name="quantity"]' ).val( 1 );
	});
	</script>
<?php
}
?>