Filter the iCal link generated by The Events Calendar Pro to use the webcal protocol instead of http

filter_ical.php

<?php
/**
 * Filter the iCal link generated by The Events Calendar Pro to use the webcal
 * protocal instead of http
 *
 * Note: if you have https:// on your site, pelase adjust accordingly
 *
 * @author  jkudish
 * @param 	string $link the original
 * @return  string $link the filtered link
 */
add_filter('tribe_get_ical_link', 'tribe_filter_ical_link');
function tribe_filter_ical_link($link) {
	return str_replace('http://', 'webcal://', $link);
}