ajaxurl error

In WP 3.8, I was getting an ajaxurl undefined error when clicking on a comment to vote it. I added ajaxurl as a var to the below code to casepress-upvote.php, and afterwards the voting worked.

add_action('wp_head', array($this, 'cpuv_ajaxurl'));

function cpuv_ajaxurl() {
?>
	<script type="text/javascript">
		var ajaxurl = '<?php echo admin_url('admin-ajax.php'); ?>';
	</script>
<?php
}

http://wordpress.org/plugins/casepress-upvote/