fix semantic relevance article title

cl-theme/templates/article.html

@@ -67,7 +67,7 @@
 
                     <!-- post header -->
                     <div class="card-content-header">
-                        <h4 class="title is-4 has-text-centered" id="titulo">{{ article.title }}</h4>
+                        <h2 class="title is-4 has-text-centered" id="titulo">{{ article.title }}</h2>
                     </div>
                     <!-- end of post header -->