Use mocha module directly, instead of gulp-mocha / Update devDependencies

* I added [mocha](https://www.npmjs.org/package/mocha) module. Currently this project use it but `devDependencies` doesn't include it.
* I removed unused [gulp-mocha](https://www.npmjs.org/package/gulp-mocha) module.
* I added [`mocha` option](https://github.com/jshint/jshint/blob/4d12de6439248a46adfae4fb9c69505168af2679/src/vars.js#L649-L662) to .jshintrc and remove `globals`.
* I updated devDependencies and add `files` field to package.json.