Unbreak the theme editor
Unbreak the theme editor

An oversight missing a change to ES class syntax caused
this.  This fixes it.

closes CORE-1148

Test Plan:
  - Load up a theme
  - Make a change and preview it
  - Save the theme
  - Apply the theme
  - Everything works without a JS error

Change-Id: Ifeff3a199518d00203be9778f566bc3988edc317
Reviewed-on: https://gerrit.instructure.com/143616
Reviewed-by: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
Tested-by: Jenkins
QA-Review: Jeremy Putnam <b030d6d6f199f844ec424882be473c2ab9adc93b@instructure.com>
Product-Review: Clay Diffrient <9dff2e5c98626d20d2848250c411e8009465bb87@instructure.com>

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