Check if session_expire_delay column exists before adding the column.

db/migrate/20150609141121_add_session_expire_delay_for_application_settings.rb

@@ -1,5 +1,7 @@
 class AddSessionExpireDelayForApplicationSettings < ActiveRecord::Migration
   def change
+    unless column_exists?(:application_settings, :session_expire_delay)
       add_column :application_settings, :session_expire_delay, :integer, default: 10080, null: false
     end
   end
+end