Show article:modified_time on article only

_includes/seo.html

@@ -98,7 +98,7 @@
   <meta property="article:published_time" content="{{ page.date | date_to_xmlschema }}">
 {% endif %}
 
-{% if page.last_modified_at %}
+{% if og_type == "article" and page.last_modified_at %}
   <meta property="article:modified_time" content="{{ page.last_modified_at | date_to_xmlschema }}">
 {% endif %}