Update dependencies / Fix .npmignore

* I removed [mocha](https://www.npmjs.org/package/mocha) from `dependencies` because it is unnecessary in production.
* I updated [map-stream](https://www.npmjs.org/package/map-stream) to v0.1.x.
* `.DS_Store` and `node_modules` are ignored by default. See the npm developer guide, [*Keeping files out of your package*](https://www.npmjs.org/doc/misc/npm-developers.html#Keeping-files-out-of-your-package).