don't give i18n a relative path

It doesn't load files relative to Rails.root

Change-Id: I926ef03cff61af4c03777ba40286fb62602edcbf
Reviewed-on: https://gerrit.instructure.com/36598
Reviewed-by: Jon Jensen <jon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>
QA-Review: Brian Palmer <brianp@instructure.com>