Updates widths to keep overlap from happening.

fixes CNVS-13924

test plan:
   - Go to a course syllabus in Chrome
   - Make sure several assignments are there with due dates
   - Resize the window to be small
   - Date and Day columns should not overlap but remain in their
     own columns.

Change-Id: I51602d4df85d5c6c07e1a987a8ea5a1852d906dd
Reviewed-on: https://gerrit.instructure.com/39558
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Hilary Scharton <hilary@instructure.com>