Add custom javascript to page head in WordPress

functions.php

<?php
add_action( 'wp_head', 'header_scripts' );

function header_scripts() {
	echo '<!--Start of Zopim Live Chat Script-->'."\n";
	echo '<script type="text/javascript">'."\n";
	echo 'window.$zopim||(function(d,s){var z=$zopim=function(c){z._.push(c)},$=z.s='."\n";
	echo 'd.createElement(s),e=d.getElementsByTagName(s)[0];z.set=function(o){z.set.'."\n";
	echo '_.push(o)};z._=[];z.set._=[];$.async=!0;$.setAttribute(\'charset\',\'utf-8\');'."\n";
	echo '$.src=\'//v2.zopim.com/?1JmbWASHEGvl7oxKGkdaQzNfQYWLE7El\';z.t=+new Date;$.'."\n";
	echo 'type=\'text/javascript\';e.parentNode.insertBefore($,e)})(document,\'script\');'."\n";
	echo '</script>'."\n";
	echo '<!--End of Zopim Live Chat Script-->'."\n";
}