use require_dependency instead in importers

Change-Id: Iaa1c085b5ec30d0e9e1d4dd698ceff935c9f604d
Reviewed-on: https://gerrit.instructure.com/37971
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>