Fix edit/delete icon visibility on hover
Fix edit/delete icon visibility on hover

.hide-till-hover class used on the edit/delete icons is
dependent on having a parent element with a class called
.hover-container

Without this patch, they only appear if you happen to
hover DIRECTLY over them, which is way too much guesswork.

refs: CNVS-8601

Test plan:
1. Add several rubrics in the course rubrics index
   (e.g. /courses/:course_id/rubrics)
2. Hover over the blank area to the right of the rubric title
3. The "links" span should be visible on hover, exposing
   the edit and delete icons

Change-Id: I32c2d6f683497a8a98a0a3625624ba9ea2301407
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/45306
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Product-Review: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>
QA-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>
Reviewed-by: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>
Reviewed-by: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>

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