rails3: second attempt at fixing erubis

Change-Id: I3bba2799e20fdd52efe6a16b1276d5cfac74419f
Reviewed-on: https://gerrit.instructure.com/30013
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Product-Review: Cameron Matheson <cameron@instructure.com>
QA-Review: Cameron Matheson <cameron@instructure.com>