Added overflow-y to the slides.

nbconvert/templates/reveal.tpl

@@ -37,6 +37,8 b' document.write( \'<link rel="stylesheet" href="reveal.js/css/print/\' + ( window.l'
 /* Overrides of notebook CSS for static HTML export */
 .reveal {
   font-size: 20px;
+overflow-y: auto;
+overflow-x: hidden;
 }
 .reveal pre {
 width: 98%;