Remove error on ICalCalendar.addEvent() for missing end time

Followup to #32.

lib/calendar.js

@@ -285,11 +285,6 @@ var ICalCalendar = function(_data) {
             throw 'event.start is a mandatory item!';
         }
 
-        // validation: end
-        if(!event.end) {
-            throw 'event.end is a mandatory item!';
-        }
-
         // validation: summary
         if(!event.summary) {
             throw 'event.summary is a mandatory item!';

test/test_0.1.x.js

@@ -185,17 +185,6 @@ describe('ical-generator 0.1.x', function() {
             }, /event\.start must be a Date Object/);
         });
 
-        it('should throw error when no end time given', function() {
-            var generator = require(__dirname + '/../lib/index.js'),
-                cal = generator();
-
-            assert.throws(function() {
-                cal.addEvent({
-                    start: new Date()
-                });
-            }, /event\.end is a mandatory item/);
-        });
-
         it('should throw error when end time is not a date', function() {
             var generator = require(__dirname + '/../lib/index.js'),
                 cal = generator();

test/test_0.2.x.js

@@ -230,6 +230,15 @@ describe('ical-generator 0.2.x / ICalCalendar', function() {
 
                 assert.equal(event.summary(), 'Patch-Day');
             });
+
+            it('should not require optional parameters', function() {
+                assert.doesNotThrow(function () {
+                    ical().addEvent({
+                        start: new Date(),
+                        summary: 'Patch-Day'
+                    });
+                }, Error);
+            });
         });
 
         describe('events()', function() {