feat(VinylNodeCollection): only output files that just changed

* same rule applied to manifest.json files
* it can reduce the file system call to minimum
* this fixes #16 

![2014-07-04 1 36 45](https://cloud.githubusercontent.com/assets/922234/3473544/06673ffa-02d9-11e4-8838-1e1d5efa9ec1.png)