open Courses & Groups dropdown on click

fixes CNVS-13379

test plan:
  * open Canvas in a mobile browser
  * click on Courses & Groups
  * verify that the courses and groups menu opens

Change-Id: I375134508f43fd681cdc7f57f446420f8bd58dc8
Reviewed-on: https://gerrit.instructure.com/35731
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Drew Bowman <dbowman@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Braden Anderson <banderson@instructure.com>