Fixes #1225

always enable highlight.js to fix markdown-only usage

index.html

@@ -399,7 +399,7 @@ Reveal.addEventListener( 'customevent', function() {
 					{ src: 'lib/js/classList.js', condition: function() { return !document.body.classList; } },
 					{ src: 'plugin/markdown/marked.js', condition: function() { return !!document.querySelector( '[data-markdown]' ); } },
 					{ src: 'plugin/markdown/markdown.js', condition: function() { return !!document.querySelector( '[data-markdown]' ); } },
-					{ src: 'plugin/highlight/highlight.js', async: true, condition: function() { return !!document.querySelector( 'pre code' ); }, callback: function() { hljs.initHighlightingOnLoad(); } },
+					{ src: 'plugin/highlight/highlight.js', async: true, callback: function() { hljs.initHighlightingOnLoad(); } },
 					{ src: 'plugin/zoom-js/zoom.js', async: true },
 					{ src: 'plugin/notes/notes.js', async: true }
 				]