Deleting Customers and/or Orders from the Demo App throws an exception

[nickcharlton]

https://sentry.io/thoughtbot-6l/administrate/issues/207094470/

PG::ForeignKeyViolation: ERROR:  update or delete on table "customers" violates foreign key constraint "fk_rails_99d97e3ae6" on table "orders"
DETAIL:  Key (id)=(14627) is still referenced from table "orders".

  active_record/connection_adapters/postgresql_adapter.rb:598:in `async_exec'
    log(sql, name, binds) { @connection.async_exec(sql, type_casted_binds) }
  active_record/connection_adapters/postgresql_adapter.rb:598:in `block in exec_no_cache'
    log(sql, name, binds) { @connection.async_exec(sql, type_casted_binds) }
  active_record/connection_adapters/abstract_adapter.rb:589:in `block in log'
    :binds          => binds) { yield }
  active_support/notifications/instrumenter.rb:21:in `instrument'
    yield payload
  active_record/connection_adapters/abstract_adapter.rb:583:in `log'
    @instrumenter.instrument(
...
(110 additional frame(s) were not displayed)

ActiveRecord::InvalidForeignKey: PG::ForeignKeyViolation: ERROR:  update or delete on table "customers" violates foreign key constraint "fk_rails_99d97e3ae6" on table "orders"
DETAIL:  Key (id)=(14627) is still referenced from table "orders".
: DELETE FROM "customers" WHERE "customers"."id" = $1

ActiveRecord::InvalidForeignKey: PG::ForeignKeyViolation: ERROR:  update or delete on table "customers" violates foreign key constraint "fk_rails_99d97e3ae6" on table "orders"
DETAIL:  Key (id)=(14627) is still referenced from table "orders".
: DELETE FROM "customers" WHERE "customers"."id" = $1