More code fence syntax highlighting

src/mermaidAPI.js

@@ -200,7 +200,7 @@ export const decodeEntities = function (text) {
 /**
  * Function that renders an svg with a graph from a chart definition. Usage example below.
  *
- * ```js
+ * ```javascript
  * mermaidAPI.initialize({
  *      startOnLoad:true
  *  });