Change migration to add only weight colum

db/migrate/20170926200545_add_board_filter_fields.rb

-class AddBoardFilterFields < ActiveRecord::Migration
-  include Gitlab::Database::MigrationHelpers
-
-  DOWNTIME = false
-
-  disable_ddl_transaction!
-
-  def up
-    add_column :boards, :weight, :integer, index: true
-    add_reference :boards, :assignee, index: true
-
-    add_concurrent_foreign_key :boards, :users, column: :assignee_id, on_delete: :nullify
-  end
-
-  def down
-    remove_column :boards, :weight
-
-    remove_foreign_key :boards, column: :assignee_id
-    remove_reference :boards, :assignee
-  end
-end

db/migrate/20170926200545_add_weight_to_boards.rb

+class AddWeightToBoards < ActiveRecord::Migration
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def change
+    add_column :boards, :weight, :integer, index: true
+  end
+end