fix typo in EXDATE

lib/event.js

@@ -703,7 +703,7 @@ var ICalEvent = function(_data, calendar) {
             }
 
             if(data.repeating.exclude) {
-                g += ';EXCLUDE=';
+                g += ';EXDATE=';
                 data.repeating.exclude.forEach(function(excludedDate) {
                     g += tools.formatDate(excludedDate);
                 });