fix stylelint, refs SD-1603
fix stylelint, refs SD-1603

test plan:
* add an invalid hex code to a css file
  ex: app/stylesheets/pages/_rubrics.scss
  color: #YARRRRRRRR
* save the file
* `script/stylelint`
* verify you see an error for this hex code

Change-Id: Iee7a0bbdae032761a7e0f1c91f2d99d469c1cb3d
Reviewed-on: https://gerrit.instructure.com/93575
Reviewed-by: Jon Jensen <44f878afe53efc66b76772bd845eb65944ed8232@instructure.com>
Product-Review: Jon Jensen <44f878afe53efc66b76772bd845eb65944ed8232@instructure.com>
QA-Review: Jon Jensen <44f878afe53efc66b76772bd845eb65944ed8232@instructure.com>
Tested-by: Jenkins

grahamb/canvas-lms,sfu/canvas-lms,matematikk-mooc/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,SwinburneOnline/canvas-lms,HotChalk/canvas-lms,HotChalk/canvas-lms,djbender/canvas-lms,grahamb/canvas-lms,HotChalk/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,venturehive/canvas-lms,instructure/canvas-lms,grahamb/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,grahamb/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,matematikk-mooc/canvas-lms,SwinburneOnline/canvas-lms,instructure/canvas-lms,HotChalk/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,grahamb/canvas-lms,matematikk-mooc/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,SwinburneOnline/canvas-lms,djbender/canvas-lms,SwinburneOnline/canvas-lms,instructure/canvas-lms,matematikk-mooc/canvas-lms