Added an alt attribute to the hidden image in app/views/quizzes/quizzes/show.html.erb for accessability
Added an alt attribute to the hidden image in
app/views/quizzes/quizzes/show.html.erb for accessability

fixes CNVS-21981

test plan
-navigate to quiz show page
-alt text should now be null for hidden image next to the
"Save It Now" button.

Change-Id: I7b29b75b45234dac21e89da6ff0b38929f96c48d
Reviewed-on: https://gerrit.instructure.com/60056
Reviewed-by: Cameron Sutter <853bcc0cb8f5834b7805e8eb9a762054be43c731@instructure.com>
Tested-by: Jenkins
QA-Review: Adam Stone <a0b2b61e2edcf99aa16080c2254a6ae6923d1fac@instructure.com>
Product-Review: Davis McClellan <af76235884e05a8dc7aff57674cbcac11e943ac3@instructure.com>

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