Optimize common assets with CDN

* jquery
* lodash
* socket.io
* boostrap

public/views/slide.ejs

@@ -87,7 +87,6 @@
             MathJax.Hub.Config({ messageStyle: "none", skipStartupTypeset: true ,tex2jax: {inlineMath: [['$','$'], ['\\(','\\)']], processEscapes: true }});
         </script>
         <% if(useCDN) { %>
-        <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
         <script src="//cdn.jsdelivr.net/velocity/1.3.1/velocity.min.js" defer></script>
         <script src="https://cdnjs.cloudflare.com/ajax/libs/js-yaml/3.6.1/js-yaml.min.js" defer></script>
         <script type="text/javascript" src="//cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML" defer></script>
@@ -102,6 +101,8 @@
         <script src="<%- url %>/vendor/moment/min/moment-with-locales.js" defer></script>
         <script src="<%- url %>/vendor/mermaid/dist/mermaid.min.js" defer></script>
         <% } %>
+        <script src="//ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
+        <script src="//cdnjs.cloudflare.com/ajax/libs/lodash.js/4.16.4/lodash.min.js" defer></script>
         <script src="//cdnjs.cloudflare.com/ajax/libs/viz.js/1.3.0/viz.js" defer></script>
         <%- include build/slide-scripts %>
     </body>