Fixes react-modal so escape key works

Makes react-modal match the current source without
an actual release from react-modal. This may
change in a future release, but the New Files
code shouldn't need any changes to accomadate the
change later.

Test Plan:
  - Open up new files
  - Open up the file preview
  - Press the escape key
  - The preview should close.

Change-Id: Ie5ff48dbeb35d89ee17c7e8cb3ae64edc0b5d252
Reviewed-on: https://gerrit.instructure.com/42320
Reviewed-by: Dan Minkevitch <dan@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Product-Review: Dan Minkevitch <dan@instructure.com>