Update devDependencies / Use SVG badge

* I updated devDependencies of package.json. Many modules used in this project is outdated.
  * From [v2.5.1](https://github.com/jshint/jshint/releases/tag/2.5.0), JSHint doesn't support `smarttabs` and `trailing` options.
* I updated the image format of the build status badge from PNG to SVG. SVG badge looks beautiful on retina displays.