Use set -e to force failure of generate_js_coverage
Use set -e to force failure of generate_js_coverage

Test Plan:
  - Introduce a failing JS test
  - Run `COVERAGE=1 RUN_TESTS_FIRST=true yarn run test:coverage`
  - It should fail

Change-Id: I27c6c876c68ce76be2da85e0e573e2051ade1951
Reviewed-on: https://gerrit.instructure.com/169389
Tested-by: Jenkins
QA-Review: Clay Diffrient <9dff2e5c98626d20d2848250c411e8009465bb87@instructure.com>
Product-Review: Clay Diffrient <9dff2e5c98626d20d2848250c411e8009465bb87@instructure.com>
Reviewed-by: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>

djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sfu/canvas-lms