fix eportfolio download

fixes CNVS-15147

test plan:
 - create an eportfolio for a user
 - download the eportfolio
 > it should download

Change-Id: I674333fed77d159201e35b7c2e6ca12a033e4856
Reviewed-on: https://gerrit.instructure.com/40412
Reviewed-by: Simon Williams <simon@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: Anna Koalenz <akoalenz@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cameron Sutter <csutter@instructure.com>