fix gear menu placement for last item in newfiles

fixes: CNVS-16866
refs: CNVS-15264

test plan:
    open new files,
    click the gear menu on the file/folder at the bottom
    of the list.
    it should appear and not be cut off

Change-Id: I56b8fc983a8aa5c78039a6a0e5cde7669b6cf89d
Reviewed-on: https://gerrit.instructure.com/44424
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Dan Minkevitch <dan@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>