SPUD Serializer ReadStream 'close' event handler

The 'close' event set on the readstream was not firing, so I switched it to the end event.  I also corrected its callback method to end the writeStream and access the correct property name ( writeStream['_data'] instead of writeStream['data'], which was undefined ).

The mocha unit tests all passed after my change, so I do not think the issue was specific to the custom serializer I am using in my project.