spec: add default stub value in audit api spec
spec: add default stub value in audit api spec

flag=none

Test Plan:
- specs pass

Change-Id: Ie5a8fd95893c1ab09f673baa603839afc281d94a
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/232352
Reviewed-by: Adrian Packel <9c6a39807293376f29cba17542b4cb1b663ecc4a@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: Spencer Olson <7cc0890d6f1f70810a023e7173eca5724d6c8e49@instructure.com>
Product-Review: Spencer Olson <7cc0890d6f1f70810a023e7173eca5724d6c8e49@instructure.com>

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