added helper function to get modification time from git

layouts/blogpost.erb

@@ -9,7 +9,7 @@
 <meta name="twitter:label1" value="Author" />
 <meta name="twitter:data1" value="<%= @item[:author] %>" />
 <meta name="twitter:label2" value="Created at" />
-<meta name="twitter:data2" value="<%= @item[:created_at] %>" />
+<meta name="twitter:data2" value="<%= gitmtime item %>" />
 <meta name="twitter:card" content="summary_large_image" />
 
 <!-- Animate.css -->

lib/helpers/blog.rb

@@ -25,4 +25,15 @@ module BlogHelper
       </figure>
     HTML
   end
+
+  def gitmtime
+    # find file extension
+    filepath=@item[:content_filename]
+    str=`git log -1 --format='%ci' -- #{filepath}`
+    if str == ""
+        return @item[:created_at]
+    else
+        return DateTime.parse( str )
+    end
+end
 end