pluralize restricted access title

fixes CNVS-16902

The title wasn't pluralize. It now is

Test Case
Given you are testing new files
When you select ONE item
And you click the 'restricted access' button
Then a dialog should appear with a title that says "Editing permissions
for 1 item"

Given you are testing new files
When you select two items
And you click the 'restricted access' button
Then a dialog should appear with a title that says "Editing permissions
for 2 items"

Change-Id: If19e1cf8b7c7df080e889cf9a74888fd48253186
Reviewed-on: https://gerrit.instructure.com/44479
Reviewed-by: Ryan Shaw <ryan@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>