Use mkdirp and rimraf directly, instead of fs-extra

* I added [mkdirp](https://github.com/substack/node-mkdirp) and [rimraf](https://github.com/isaacs/rimraf), and removed [fs-extra](https://github.com/jprichardson/node-fs-extra). This project doesn't need the gazillions of fs-extra's methods.
* I updated [chai](http://chaijs.com/) to v1.10.0.