Update dependencies and .jshintrc

* I updated [graceful-fs](https://www.npmjs.org/package/graceful-fs) and [mocha](https://www.npmjs.org/package/mocha).
* [grunt-contrib-jshint](https://github.com/gruntjs/grunt-contrib-jshint) v0.10.0 depends on JSHint `~2.5.0`.

  * According to [the release note](https://github.com/jshint/jshint/releases) of JSHint v2.5.0:
    > The following options were **removed**: nomen, onevar, passfail, white, gcl, smarttabs, trailing.

  * JSHint v2.5.0 supports [the `mocha` option](https://github.com/jshint/jshint/pull/1597) so we don't need to specify the predefined variables of Mocha explicitly.