Fix string generator to include commas.

- Just realized I forgot this.

lib/event.js

@@ -704,9 +704,11 @@ var ICalEvent = function(_data, calendar) {
 
             if(data.repeating.exclude) {
                 g += ';EXDATE=';
+                var sArr = [];
                 data.repeating.exclude.forEach(function(excludedDate) {
-                    g += tools.formatDate(excludedDate);
+                    sArr.push(tools.formatDate(excludedDate));
                 });
+                g += sArr.join(',');
             }
 
             g += '\r\n';