add timestamp

lib/pleroma/elasticsearch/document_mappings/hashtag.ex

@@ -1,10 +1,17 @@
 defmodule Pleroma.Elasticsearch.DocumentMappings.Hashtag do
   def id(obj), do: obj.id
 
-  def encode(hashtag) do
+  def encode(%{timestamp: _} = hashtag) do
     %{
       hashtag: hashtag.name,
       timestamp: hashtag.timestamp     
     } 
   end
+
+  def encode(hashtag) do
+    %{
+      hashtag: hashtag.name,
+      timestamp: hashtag.inserted_at
+    }
+  end
 end