bump rails to 2.3.18
bump rails to 2.3.18

fixes CNVS-4745

changelog is at https://github.com/rails/rails/commits/v2.3.18

Change-Id: Ice2b9ab302965ca69b3e59f336900b106d694605
Reviewed-on: https://gerrit.instructure.com/18957
Reviewed-by: Brian Palmer <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@instructure.com>
Product-Review: Brian Palmer <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@instructure.com>
QA-Review: Brian Palmer <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@instructure.com>
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>

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