fix checkbox labels on files
fix checkbox labels on files

test plan:
 - using VO with Safari, go to the files page
 - the checkbox that appears when you tab to a file
   (to allow keyboard multi-select) should be labeled
   "Select (name of file)"

fixes ADMIN-2617

Change-Id: I19d751b547ff207821a1f1a848ae5d6e5daa10e5
Reviewed-on: https://gerrit.instructure.com/192412
Tested-by: Jenkins
Reviewed-by: Carl Kibler <7c2b40129dd885a147d5b2dda56dda016b9a8f57@instructure.com>
QA-Review: Daniel Sasaki <ae19fabf7fe19dff310008c9b6a4d2ec84d311d8@instructure.com>
Product-Review: Daniel Sasaki <ae19fabf7fe19dff310008c9b6a4d2ec84d311d8@instructure.com>

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