Add site_description to meta description tag for real

Author: nlalonde

app/views/layouts/application.html.erb

@@ -4,7 +4,7 @@
     <meta charset="utf-8">
     <title><%= content_for?(:title) ? yield(:title) + ' - ' + SiteSetting.title : SiteSetting.title %></title>
     <meta content="width=device-width, initial-scale=1.0" name="viewport">
-    <meta content="<%= @description %>" name="description">
+    <meta content="<%= SiteSetting.site_description %>" name="description">
     <meta content="" name="author">
 
     <%= canonical_link_tag %>