Use map-stream directly, instead of event-stream

* I replaced [event-stream](https://github.com/dominictarr/event-stream) with [map-stream](https://github.com/dominictarr/map-stream), because [es.map()](https://github.com/dominictarr/event-stream#map-asyncfunction) is [just an alias to map-stream](https://github.com/dominictarr/event-stream/blob/480c38d08f5dffa34c41ac737456a3ea98f58d04/index.js#L12).
* I fixed a typo in .travis.yml. ("10.0" -> "0.10")
* I removed the globals in .jshintrc. Instead, I added `mocha` option.
* I updated [chai](http://chaijs.com/), [mocha](http://visionmedia.github.io/mocha/) and [gulp-util](https://github.com/gulpjs/gulp-util).
* I updated .npmignore.
  * `.DS_Store`, `npm-debug.log` 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).
* I changed the image format of badges in README. SVG badges look beautiful on retina displays.