fix typo in attachment preview helper
fix typo in attachment preview helper

fixes #10913

Test plan:
  * go to a student's assignment submission page (for a submission that
    can be previewed in crocodoc)
  * click the preview button and make sure that you can annotate the
    document

Change-Id: Ic1b62b4f6a626d9f1f17541e137c3381350c651a
Reviewed-on: https://gerrit.instructure.com/13946
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>

djbender/canvas-lms,arrivu/jigsaw-lms,Unow/ins,shidao-fm/canvas-lms,arrivu/hoodemo,venturehive/canvas-lms,va7map/canvas-lms,tgroshon/canvas-lms,AndranikMarkosyan/lms,sdeleon28/canvas-lms,loganrun/pincan,wrdsb/canvas-lms,leftplusrightllc/canvas-lms,parbros/red-innovadores-lms,grahamb/canvas-lms,ShreniiNepal/shrenii_lmp,shidao-fm/canvas-lms,roxolan/canvas-lms,usmschuck/canvas,arrivu/hoodemo,instructure/canvas-lms,arrivu/qibla-ecampus,djbender/canvas-lms,wimemx/Canvas,greyhwndz/canvas-lms,efrj/canvas-lms,arrivu/hiring-site,wye0220/shindig-canvas,parbros/red-innovadores-lms,venturehive/canvas-lms,arrivu/hiring-site,SwinburneOnline/canvas-lms,utkarshx/canvas-lms,rup/Tarrax,arrivu/jigsaw-lms,greyhwndz/canvas-lms,instructure/canvas-lms,parbros/red-innovadores-lms,merichar/canvas-lms,jay3126/canvas-lms,kyroskoh/canvas-lms,landonwilkins/canvas-lms,fronteerio/canvas-lms,merichar/canvas-lms,va7map/canvas-lms,narigone/canvas,redconfetti/canvas-lms,sfu/canvas-lms,whalejasmine/canvas-lms,HotChalk/canvas-lms,sli7246/canvas_branch,whalejasmine/canvas-lms,wimemx/Canvas,leftplusrightllc/canvas-lms,jay3126/canvas-lms,greyhwndz/canvas-lms,Rvor/canvas-lms,loganrun/pincan,sfu/canvas-lms,arrivu/hoodemo,grahamb/canvas-lms,landonwilkins/canvas-lms,usmschuck/canvas,usmschuck/canvas,Unow/ins,wye0220/shindig-canvas,nditech/red-innovadores-lms,antoniuslin/canvas-lms,whalejasmine/canvas-lms,samuels410/greatlakes-lms,instructure/canvas-lms,matematikk-mooc/canvas-lms,eCNAP/CANVAS,Rvor/canvas-lms,SwinburneOnline/canvas-lms,sfu/canvas-lms,kyroskoh/canvas-lms,samuels410/greatlakes-lms,sfu/canvas-lms,narigone/canvas,ShreniiNepal/shrenii_lmp,rup/Tarrax,skmezanul/canvas-lms,greyhwndz/canvas-lms,utkarshx/canvas-lms,arrivu/arrivu-lms,wrdsb/canvas-lms,instructure/canvas-lms,arrivu/jigsaw-lms,tgroshon/canvas-lms,SwinburneOnline/canvas-lms,dgynn/canvas-lms,wye0220/shindig-canvas,sfu/canvas-lms,venturehive/canvas-lms,tgroshon/canvas-lms,skmezanul/canvas-lms,nditech/red-innovadores-lms,wrdsb/canvas-lms,Unow/canvas-lms,landonwilkins/canvas-lms,juoni/canvas-lms,instructure/canvas-lms,va7map/canvas-lms,antoniuslin/canvas-lms,gbleydon/canvas-lms,arrivu/arrivu-lms,ShreniiNepal/shrenii_lmp,juoni/canvas-lms,roxolan/canvas-lms,djbender/canvas-lms,Jyaasa/canvas-lms,whalejasmine/canvas-lms,grahamb/canvas-lms,sli7246/canvas_branch,merichar/canvas-lms,usmschuck/canvas,wrdsb/canvas-lms,leftplusrightllc/canvas-lms,Jyaasa/canvas-lms,roxolan/canvas-lms,snehakachroo1/LSI_replica,matematikk-mooc/canvas-lms,narigone/canvas,antoniuslin/canvas-lms,sdeleon28/canvas-lms,Rvor/canvas-lms,dgynn/canvas-lms,kyroskoh/canvas-lms,AndranikMarkosyan/lms,matematikk-mooc/canvas-lms,Jyaasa/canvas-lms,snehakachroo1/LSI_replica,eCNAP/CANVAS,skmezanul/canvas-lms,instructure/canvas-lms,eCNAP/CANVAS,eCNAP/CANVAS,skmezanul/canvas-lms,gbleydon/canvas-lms,jay3126/canvas-lms,tgroshon/canvas-lms,landonwilkins/canvas-lms,fronteerio/canvas-lms,SwinburneOnline/canvas-lms,samuels410/greatlakes-lms,nditech/red-innovadores-lms,HotChalk/canvas-lms,fronteerio/canvas-lms,utkarshx/canvas-lms,utkarshx/canvas-lms,Unow/ins,shidao-fm/canvas-lms,AndranikMarkosyan/lms,arrivu/qibla-ecampus,wimemx/Canvas,sdeleon28/canvas-lms,ShreniiNepal/shrenii_lmp,Unow/canvas-lms,leftplusrightllc/canvas-lms,arrivu/hiring-site,juoni/canvas-lms,Jyaasa/canvas-lms,snehakachroo1/LSI_replica,kyroskoh/canvas-lms,antoniuslin/canvas-lms,fronteerio/canvas-lms,efrj/canvas-lms,samuels410/greatlakes-lms,instructure/canvas-lms,HotChalk/canvas-lms,narigone/canvas,va7map/canvas-lms,Unow/canvas-lms,redconfetti/canvas-lms,venturehive/canvas-lms,dgynn/canvas-lms,nditech/red-innovadores-lms,djbender/canvas-lms,efrj/canvas-lms,sfu/canvas-lms,dgynn/canvas-lms,efrj/canvas-lms,shidao-fm/canvas-lms,grahamb/canvas-lms,redconfetti/canvas-lms,HotChalk/canvas-lms,AndranikMarkosyan/lms,Rvor/canvas-lms,matematikk-mooc/canvas-lms,arrivu/arrivu-lms,sli7246/canvas_branch,juoni/canvas-lms,grahamb/canvas-lms,arrivu/qibla-ecampus,gbleydon/canvas-lms,redconfetti/canvas-lms,roxolan/canvas-lms,jay3126/canvas-lms,loganrun/pincan,sdeleon28/canvas-lms,snehakachroo1/LSI_replica,sfu/canvas-lms,rup/Tarrax