fix(highlight): allow pre fragments

plugin/highlight/plugin.js

@@ -35,7 +35,7 @@ const Plugin = {
 
 		Array.from( reveal.getRevealElement().querySelectorAll( 'pre code' ) ).forEach( block => {
 
-			block.parentNode.className = 'code-wrapper';
+			block.parentNode.classList.add('code-wrapper');
 
 			// Code can optionally be wrapped in script template to avoid
 			// HTML being parsed by the browser (i.e. when you need to

test/test-markdown.html

@@ -281,6 +281,15 @@
 						```
 					</script>
 				</section>
+				<section data-markdown class="with-code-in-fragment">
+					<script type="text/template">
+					  ```js
+					  foo.bar();
+					  ```
+  
+					  <!-- .element: class="fragment" -->
+					</script>
+				  </section>
 			</div>
 		</div>
 
@@ -453,6 +462,11 @@
 					assert.strictEqual( deck6.getRevealElement().querySelectorAll( '.with-line-highlights-and-lanugage .hljs.javascript[data-line-numbers="1,2,3"]' ).length, 1 );
 				});
 
+				
+				QUnit.test( '```block should allow custom fragment', function( assert ) {
+					assert.strictEqual( deck5.getRevealElement().querySelectorAll( '.with-code-in-fragment pre.fragment' ).length, 1 );
+				});
+
 			} );
 
 			deck1.initialize();