Serkan

Fix missing handling of undefined items in pbxWriter.prototype.writeArray

1

Fix for https://github.com/alunny/node-xcode/issues/71

I am using a [deep-diff](https://github.com/flitbit/diff) library to compare resulting objects from `xcode.project(file).parseSync()`. I was getting some undefined items at https://github.com/alunny/node-xcode/blob/master/lib/pbxWriter.js#L183 when I ran `project.writeSync()`. I already have a fix, will...

Also referenced here https://github.com/hueniverse/postmile/issues/18