Removes gulp-rimraf from gulpfile in favor of del()

Related to https://github.com/h5bp/html5-boilerplate/issues/1578
> SublimeLinter is too good :package: 

Don't know why the vim JSHint plugin didn't catch that... maybe it's time to improve the `gulpfile.js` to also lint the non `src/` files hehe.

 .jshintrc