Fix site_name meta property (#27)

Author: erxclau

index.html

@@ -7,7 +7,7 @@
 
     <meta property="og:url" content="{{ config.deployment }}" />
     <meta property="og:type" content="website" />
-    <meta property="og:site_name" content="{{ content.hed }}" />
+    <meta property="og:site_name" content="{{ config.hed }}" />
     <meta property="og:title" content="{{ config.hed }}" />
     <meta property="og:description" content="{{ config.dek }}" />
     <meta property="og:image" content="{{ config.social_img }}" />