Fix which node version is required
Fix which node version is required

In `package.json` engine is set to `>=9.0.0`.
tehfedaykin/10CommandmentsofCommunityOrganizing,10xEngineer/reveal.js,lecovi/reveal.js,Jean85/reveal.js,siddhartha-gadgil/presentations,maximesinclair/presentations,rbtcollins/reveal.js,rbtcollins/reveal.js,Jean85/reveal.js,maximesinclair/presentations,rbtcollins/reveal.js,tehfedaykin/10CommandmentsofCommunityOrganizing,rbtcollins/reveal.js,lvh/reveal.js,kenkunz/js-crash-course,hakimel/reveal.js,jayramj/agile-retro,dbs/reveal.js,hakimel/reveal.js,seefood/DIYHolidays,lecovi/reveal.js,lvh/reveal.js,siddhartha-gadgil/presentations,jayramj/agile-retro,dbs/reveal.js,lecovi/reveal.js,rbtcollins/reveal.js,seefood/DIYHolidays,10xEngineer/reveal.js,kenkunz/js-crash-course,rbtcollins/reveal.js,siddhartha-gadgil/presentations