update minimum supported safari, chrome and firefox
update minimum supported safari, chrome and firefox

test-plan:
* with chrome 31 & 32, verify browser warning does not display
* with safari 6 & 7, verify browser warning does not display
* with firefox 26 & 27, verify browser warning does not display

Change-Id: I8b5250908bfb0269d3616fbf06a5e6da65e016c3
Reviewed-on: https://gerrit.instructure.com/28717
Reviewed-by: Bryan Madsen <0a3ba1af216659500dd8f41e29f3979f42452870@instructure.com>
Product-Review: Bryan Madsen <0a3ba1af216659500dd8f41e29f3979f42452870@instructure.com>
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
QA-Review: Caleb Guanzon <54fa1f30d451e4f3c341a8f3c47c9215fd0be9c6@instructure.com>

usmschuck/canvas,venturehive/canvas-lms,djbender/canvas-lms,jay3126/canvas-lms,Unow/canvas-lms,shidao-fm/canvas-lms,wrdsb/canvas-lms,grahamb/canvas-lms,antoniuslin/canvas-lms,Unow/canvas-lms,redconfetti/canvas-lms,jay3126/canvas-lms,skmezanul/canvas-lms,efrj/canvas-lms,roxolan/canvas-lms,skmezanul/canvas-lms,Rvor/canvas-lms,djbender/canvas-lms,usmschuck/canvas,wrdsb/canvas-lms,skmezanul/canvas-lms,juoni/canvas-lms,leftplusrightllc/canvas-lms,Unow/canvas-lms,wrdsb/canvas-lms,tgroshon/canvas-lms,redconfetti/canvas-lms,samuels410/greatlakes-lms,redconfetti/canvas-lms,tgroshon/canvas-lms,sfu/canvas-lms,juoni/canvas-lms,sdeleon28/canvas-lms,wrdsb/canvas-lms,va7map/canvas-lms,kyroskoh/canvas-lms,arrivu/hoodemo,ShreniiNepal/shrenii_lmp,sdeleon28/canvas-lms,tgroshon/canvas-lms,sfu/canvas-lms,greyhwndz/canvas-lms,arrivu/arrivu-lms,HotChalk/canvas-lms,antoniuslin/canvas-lms,fronteerio/canvas-lms,redconfetti/canvas-lms,fronteerio/canvas-lms,leftplusrightllc/canvas-lms,Rvor/canvas-lms,shidao-fm/canvas-lms,sdeleon28/canvas-lms,greyhwndz/canvas-lms,venturehive/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,usmschuck/canvas,kyroskoh/canvas-lms,kyroskoh/canvas-lms,efrj/canvas-lms,sfu/canvas-lms,ShreniiNepal/shrenii_lmp,sdeleon28/canvas-lms,HotChalk/canvas-lms,sfu/canvas-lms,antoniuslin/canvas-lms,arrivu/hoodemo,shidao-fm/canvas-lms,va7map/canvas-lms,skmezanul/canvas-lms,SwinburneOnline/canvas-lms,va7map/canvas-lms,samuels410/greatlakes-lms,arrivu/arrivu-lms,samuels410/greatlakes-lms,jay3126/canvas-lms,sfu/canvas-lms,utkarshx/canvas-lms,Rvor/canvas-lms,efrj/canvas-lms,SwinburneOnline/canvas-lms,roxolan/canvas-lms,HotChalk/canvas-lms,va7map/canvas-lms,grahamb/canvas-lms,fronteerio/canvas-lms,roxolan/canvas-lms,whalejasmine/canvas-lms,whalejasmine/canvas-lms,wye0220/shindig-canvas,tgroshon/canvas-lms,grahamb/canvas-lms,grahamb/canvas-lms,greyhwndz/canvas-lms,arrivu/arrivu-lms,Rvor/canvas-lms,roxolan/canvas-lms,sfu/canvas-lms,HotChalk/canvas-lms,whalejasmine/canvas-lms,SwinburneOnline/canvas-lms,SwinburneOnline/canvas-lms,arrivu/hoodemo,fronteerio/canvas-lms,samuels410/greatlakes-lms,Jyaasa/canvas-lms,ShreniiNepal/shrenii_lmp,whalejasmine/canvas-lms,kyroskoh/canvas-lms,utkarshx/canvas-lms,djbender/canvas-lms,efrj/canvas-lms,shidao-fm/canvas-lms,leftplusrightllc/canvas-lms,leftplusrightllc/canvas-lms,utkarshx/canvas-lms,wye0220/shindig-canvas,Jyaasa/canvas-lms,wye0220/shindig-canvas,grahamb/canvas-lms,antoniuslin/canvas-lms,venturehive/canvas-lms,djbender/canvas-lms,usmschuck/canvas,juoni/canvas-lms,utkarshx/canvas-lms,jay3126/canvas-lms,juoni/canvas-lms,Jyaasa/canvas-lms,ShreniiNepal/shrenii_lmp,greyhwndz/canvas-lms,Jyaasa/canvas-lms