correct submission_history list for display

fixes CNVS-8721

test plan:
1. As a student, submit an assignment multiple times
2. Click on the speech bubble for the assignment in the Gradebook
3. Note that the submission times for the first and last
   submissions do not match

Change-Id: I64c1a7d56c0aacd97ab26378b16b2e2baab1656a
Reviewed-on: https://gerrit.instructure.com/45671
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cameron Sutter <csutter@instructure.com>
Reviewed-by: Josh Simpson <jsimpson@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Matt Fairbourn <mfairbourn@instructure.com>