fix the issue that code blocks in markdown are rendered as placeholde…

…r after disabling nunjucks

lib/hexo/post.js

@@ -270,10 +270,12 @@ Post.prototype.render = function(source, data = {}, callback) {
       engine: data.engine,
       toString: true,
       onRenderEnd(content) {
-        if (disableNunjucks) return content;
         // Replace cache data with real contents
         data.content = cacheObj.loadContent(content);
 
+        // Return content after replace the placeholders
+        if (disableNunjucks) return data.content;
+
         // Render with Nunjucks
         return tag.render(data.content, data);
       }