simple node-sass update which fixes this issue

I added the same jshint configuration/rules in package.json and I replaced some old function with arrow function to improve legibility

I have created a gulpfile.js with the same tasks of grunt, replaced npm script and finally ad .jshintrc for jshint

Closes #1226, #1538.

The `reveal.js` npm module is typically installed to access the CSS/JS
assets for Reveal.js. For those that want to run the plugins, they would
clone the whole repository. Hence, it doesn’t make sense to include
those as `dependencies`, which will increase download times.

Closes #1734.