spec: add tiny-mce subscript button check
spec: add tiny-mce subscript button check

Change-Id: I1842a3de1a7ade2bd9ed8d8369b6ab804c4661de
Reviewed-on: https://gerrit.instructure.com/68068
Tested-by: Jenkins
Product-Review: Jeremy Putnam <b030d6d6f199f844ec424882be473c2ab9adc93b@instructure.com>
QA-Review: Jeremy Putnam <b030d6d6f199f844ec424882be473c2ab9adc93b@instructure.com>
Reviewed-by: Michael Hargiss <59e3fde81b8d9a4f5e0cc016a3c2695591912604@instructure.com>

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