fix bad link in enrollment acceptance notification

fixes CNVS-14983

Test plan
- As a student
 - Accept enrollment to receive notification
- As a teacher
 - verify that the link in the notification takes you to the user's page

Change-Id: Ic3a7dc90e974a324666b51b81e767d0efe85a7dc
Reviewed-on: https://gerrit.instructure.com/39815
Reviewed-by: Brad Horrocks <bhorrocks@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Reviewed-by: Matthew Wheeler <mwheeler@instructure.com>
Product-Review: Ian Hoerner <ian@instructure.com>