fix semantic HTML

cl-theme/templates/base.html

@@ -108,7 +108,7 @@
         <!-- end page header -->
 
         <!-- page content -->
-        <div class="main-content">
+        <main class="main-content">
             {%- block content -%}
                 <div class="container">
                     <!-- start of posts -->
@@ -190,7 +190,7 @@
                 {% include "pagination.html" %}
                 <!-- end of pagination -->
             {%- endblock -%}
-        </div>
+        </main>
         <!-- end of page content -->
         <!-- .site-content -->