feat(jshintrc): allows the use of config file .jshintrc

The jshint option can now be the path to the '.jshintrc' config file :
```javascript
var jshint = require('gulp-jshint');

gulp.task('lint', function() {
  gulp.src('./lib/*.js')
    .pipe(jshint('./lib/.jshintrc'))
    .pipe(jshint.reporter('YOUR_REPORTER_HERE'));
});
```
Merge pull request #6 from douglasduteil/feat-use-config-file

feat(jshintrc): allows the use of config file .jshintrc