spec: restore js error capturing
spec: restore js error capturing

fix regression in 5f04437

test plan:
1. confirm you once again see lots of "JS Error" lines in the output
   :sadpanda:

Change-Id: Iafea775e5ea2570041c8a42cae6fed280caf5475
Reviewed-on: https://gerrit.instructure.com/82397
Tested-by: Jenkins
Reviewed-by: Landon Wilkins <e219b0c23c4256074cdfc7a23138e4f17200b08f@instructure.com>
Product-Review: Landon Wilkins <e219b0c23c4256074cdfc7a23138e4f17200b08f@instructure.com>
QA-Review: Landon Wilkins <e219b0c23c4256074cdfc7a23138e4f17200b08f@instructure.com>

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