journal: use updated_on for last modified time

This fixes needless outdated detection by
full_text_search:synchronize.

Author: kou

lib/full_text_search/journal_mapper.rb

@@ -49,7 +49,7 @@ def upsert_fts_target(options={})
       tag_ids << Tag.tracker(issue.tracker_id).id if issue.tracker_id
       tag_ids << Tag.issue_status(issue.status_id).id if issue.status_id
       fts_target.tag_ids = tag_ids
-      fts_target.last_modified_at = @record.created_on
+      fts_target.last_modified_at = @record.updated_on
       fts_target.registered_at = @record.created_on
       fts_target.save!
     end

test/unit/full_text_search/journal_test.rb

@@ -24,7 +24,7 @@ def test_save
                        "project_id" => issue.project_id,
                        "source_id" => journal.id,
                        "source_type_id" => Type.journal.id,
-                       "last_modified_at" => journal.created_on,
+                       "last_modified_at" => journal.updated_on,
                        "registered_at" => journal.created_on,
                        "title" => null_string,
                        "tag_ids" => [