typo with in code, replace date.toTime with date.getTime

Summary:There is no toTime method on a Date object, It should be getTime.
Closes #6054

Differential Revision: D2971217

fb-gh-sync-id: 4140be25f0704f251cc0e2f47db8fa83992dc0f0
shipit-source-id: 4140be25f0704f251cc0e2f47db8fa83992dc0f0

Author: xing-zheng

docs/NativeModulesIOS.md

@@ -133,7 +133,7 @@ and call it from JavaScript:
 ```javascript
 CalendarManager.addEvent('Birthday Party', {
   location: '4 Privet Drive, Surrey',
-  time: date.toTime(),
+  time: date.getTime(),
   description: '...'
 })
 ```