add vertical-gradiant sass mixin, works in ie7
add vertical-gradiant sass mixin, works in ie7

Change-Id: I86e685a30b7a01379b26daae0ebda0c2f4eb4d8d
Reviewed-on: https://gerrit.instructure.com/2191
Tested-by: Hudson <dfb64870173313a9a7b56f814c8e3b33e268497a@instructure.com>
Reviewed-by: Brian Whitmer <760e7dab2836853c63805033e514668301fa9c47@instructure.com>

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