Fix issues with latest ruby/jekyll version

[jwillmer]

• config.yml rename gem to plugins
• _pages/cv.html change {{site.data.cv.[page.author] }} to {{site.data.cv[page.author] }}
• _layouts/about.html change {{site.data.cv.[page.author] }} to {{site.data.authors.[page.author] }}
• check backward compatibility
• update current top 20 development languages in prism (Arduino?)
  • Update with: http://prismjs.com/download.html?#themes=prism&languages=markup+css+clike+javascript+c+csharp+bash+batch+cpp+aspnet+arduino+coffeescript+ruby+git+java+json+less+objectivec+php+powershell+python+scss&plugins=line-highlight+line-numbers
  • Note: Uncaught TypeError: Cannot read property 'tokenizePlaceholders' of undefined PrismJS/prism#1423
  • Add to ovverride.scss: pre code { display:block; width:90%; max-width:650px; margin:auto; }
• remove prism from css folder (duplicate)