fix dnd move in IE 10

fixes: CNVS-16386

test plan:
in IE10 and a couple other browsers we support,
go to newfiles
drag-n-drop a folder in the main pain to move it
to something in the left pane.
it should work

Change-Id: Idb078a7aad13528506ed44e20a77ae16f80cbb30
Reviewed-on: https://gerrit.instructure.com/43555
Reviewed-by: Dan Minkevitch <dan@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>