groups: fix group leader outcome alignment in Firefox

fixes CNVS-13366

test plan:
  * open a course's groups page
  * make a user a group leader
  * verify that the leader icon looks right across browsers

Change-Id: I73ae8f15cbbcf55a864cc4db81382b1820cea52b
Reviewed-on: https://gerrit.instructure.com/35707
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Drew Bowman <dbowman@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Braden Anderson <banderson@instructure.com>