don't call l() directly, use date_string
don't call l() directly, use date_string

changes the format slightly (uses medium instead of long), but was
blowing up on nil dates otherwise.

Change-Id: Ieae122c8a48e085b798c5643d869ee27f87c481c
Reviewed-on: https://gerrit.instructure.com/4571
Reviewed-by: JT Olds <0857133ffcd232122dc51ad55bf5fcc9d60af5d3@instructure.com>
Tested-by: Hudson <dfb64870173313a9a7b56f814c8e3b33e268497a@instructure.com>

sdeleon28/canvas-lms,leftplusrightllc/canvas-lms,greyhwndz/canvas-lms,va7map/canvas-lms,HotChalk/canvas-lms,juoni/canvas-lms,wye0220/shindig-canvas,gbleydon/canvas-lms,merichar/canvas-lms,usmschuck/canvas,Unow/ins,whalejasmine/canvas-lms,efrj/canvas-lms,sdeleon28/canvas-lms,fronteerio/canvas-lms,icelab/canvas,skmezanul/canvas-lms,arrivu/hiring-site,em2/canvas-lms,djbender/canvas-lms,em2/canvas-lms,matematikk-mooc/canvas-lms,redconfetti/canvas-lms,antoniuslin/canvas-lms,instructure/canvas-lms,kyroskoh/canvas-lms,dgynn/canvas-lms,tgroshon/canvas-lms,leftplusrightllc/canvas-lms,eCNAP/CANVAS,SwinburneOnline/canvas-lms,sfu/canvas-lms,ShreniiNepal/shrenii_lmp,HotChalk/canvas-lms,leftplusrightllc/canvas-lms,ShreniiNepal/shrenii_lmp,loganrun/pincan,landonwilkins/canvas-lms,sli7246/canvas_branch,fronteerio/canvas-lms,ankithbti/canvas_lms,skmezanul/canvas-lms,Unow/ins,HotChalk/canvas-lms,Unow/ins,snehakachroo1/LSI_replica,usmschuck/canvas,fronteerio/canvas-lms,arrivu/arrivu-lms,rup/Tarrax,matematikk-mooc/canvas-lms,gbleydon/canvas-lms,Unow/canvas-lms,parbros/red-innovadores-lms,dgynn/canvas-lms,parbros/red-innovadores-lms,arrivu/qibla-ecampus,Jyaasa/canvas-lms,merichar/canvas-lms,greyhwndz/canvas-lms,ankithbti/canvas_lms,Rvor/canvas-lms,jay3126/canvas-lms,narigone/canvas,arrivu/jigsaw-lms,ottenhoff/canvas-lms,ShreniiNepal/shrenii_lmp,Rvor/canvas-lms,sdeleon28/canvas-lms,Jyaasa/canvas-lms,rup/Tarrax,antoniuslin/canvas-lms,AndranikMarkosyan/lms,icelab/canvas,djbender/canvas-lms,va7map/canvas-lms,ottenhoff/canvas-lms,sdeleon28/canvas-lms,nditech/red-innovadores-lms,arrivu/qibla-ecampus,juoni/canvas-lms,loganrun/pincan,grahamb/canvas-lms,SwinburneOnline/canvas-lms,dgynn/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,efrj/canvas-lms,grahamb/canvas-lms,utkarshx/canvas-lms,narigone/canvas,wrdsb/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,AndranikMarkosyan/lms,landonwilkins/canvas-lms,wrdsb/canvas-lms,narigone/canvas,arrivu/hoodemo,utkarshx/canvas-lms,Rvor/canvas-lms,wye0220/shindig-canvas,shidao-fm/canvas-lms,djbender/canvas-lms,juoni/canvas-lms,roxolan/canvas-lms,roxolan/canvas-lms,icelab/canvas,redconfetti/canvas-lms,samuels410/greatlakes-lms,instructure/canvas-lms,SwinburneOnline/canvas-lms,snehakachroo1/LSI_replica,loganrun/pincan,sfu/canvas-lms,whalejasmine/canvas-lms,faraazkhan/canvas,instructure/canvas-lms,jay3126/canvas-lms,shidao-fm/canvas-lms,grahamb/canvas-lms,shidao-fm/canvas-lms,Rvor/canvas-lms,leftplusrightllc/canvas-lms,Jyaasa/canvas-lms,arrivu/jigsaw-lms,arrivu/arrivu-lms,Jyaasa/canvas-lms,rup/Tarrax,matematikk-mooc/canvas-lms,usmschuck/canvas,skmezanul/canvas-lms,redconfetti/canvas-lms,samuels410/greatlakes-lms,tgroshon/canvas-lms,sfu/canvas-lms,ankithbti/canvas_lms,fronteerio/canvas-lms,nditech/red-innovadores-lms,Unow/canvas-lms,jay3126/canvas-lms,samuels410/greatlakes-lms,em2/canvas-lms,venturehive/canvas-lms,arrivu/hiring-site,wye0220/shindig-canvas,ottenhoff/canvas-lms,utkarshx/canvas-lms,landonwilkins/canvas-lms,shidao-fm/canvas-lms,eCNAP/CANVAS,greyhwndz/canvas-lms,snehakachroo1/LSI_replica,arrivu/jigsaw-lms,HotChalk/canvas-lms,snehakachroo1/LSI_replica,landonwilkins/canvas-lms,jay3126/canvas-lms,grahamb/canvas-lms,kyroskoh/canvas-lms,wrdsb/canvas-lms,redconfetti/canvas-lms,sli7246/canvas_branch,antoniuslin/canvas-lms,AndranikMarkosyan/lms,whalejasmine/canvas-lms,eCNAP/CANVAS,arrivu/hiring-site,grahamb/canvas-lms,wimemx/Canvas,Unow/canvas-lms,antoniuslin/canvas-lms,instructure/canvas-lms,greyhwndz/canvas-lms,venturehive/canvas-lms,wimemx/Canvas,djbender/canvas-lms,AndranikMarkosyan/lms,gbleydon/canvas-lms,wimemx/Canvas,parbros/red-innovadores-lms,kyroskoh/canvas-lms,sli7246/canvas_branch,efrj/canvas-lms,roxolan/canvas-lms,instructure/canvas-lms,nditech/red-innovadores-lms,va7map/canvas-lms,tgroshon/canvas-lms,faraazkhan/canvas,samuels410/greatlakes-lms,utkarshx/canvas-lms,wrdsb/canvas-lms,va7map/canvas-lms,venturehive/canvas-lms,efrj/canvas-lms,arrivu/qibla-ecampus,ShreniiNepal/shrenii_lmp,tgroshon/canvas-lms,whalejasmine/canvas-lms,kyroskoh/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,merichar/canvas-lms,usmschuck/canvas,arrivu/arrivu-lms,dgynn/canvas-lms,faraazkhan/canvas,arrivu/hoodemo,eCNAP/CANVAS,matematikk-mooc/canvas-lms,juoni/canvas-lms,skmezanul/canvas-lms,SwinburneOnline/canvas-lms,roxolan/canvas-lms,arrivu/hoodemo,narigone/canvas,nditech/red-innovadores-lms,instructure/canvas-lms