So it turns out when you are offline an SocketError will be raised and when the response is an 404 an HTTPError will be raised. Rescue both of them now.

Author: gr4y

lib/jekyll-gist/gist_tag.rb

@@ -66,6 +66,8 @@ def fetch_raw_code(gist_id, filename = nil)
           open(uri).read.chomp
         rescue SocketError
           nil
+        rescue OpenURI::HTTPError
+          nil
         end
       end
     end