prevent scrollbars on rubric ratings in firefox
prevent scrollbars on rubric ratings in firefox

closes OUT-2324

Test plan:
Using Firefox:
- create a rubric aligned to an outcome
- assess a student using that rubric
- visit sLMGB, verify that rubric criterion
  for the assessed assignment does not show
  vertical scrollbars and does show all relevant
  content

Change-Id: I641dac42a617029b678170204266519553e964ee
Reviewed-on: https://gerrit.instructure.com/154355
Tested-by: Jenkins
Reviewed-by: Augusto Callejas <7d9b9fd126d23d111f693e51511b33ea0e7192f6@instructure.com>
QA-Review: Augusto Callejas <7d9b9fd126d23d111f693e51511b33ea0e7192f6@instructure.com>
Product-Review: Sidharth Oberoi <b9947257dd0ff1b6a5d899864f5ca846b60f0be3@instructure.com>

instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms