spec: make mention data slightly better defined
spec: make mention data slightly better defined

Change-Id: I4b87006ebf948f1af3a06bd88693f595fe8cc235
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/266112
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Mauricio Ribeiro <0f77808e58545ae2902769fbb485ffaf122ea8a5@instructure.com>
QA-Review: Mauricio Ribeiro <0f77808e58545ae2902769fbb485ffaf122ea8a5@instructure.com>
Product-Review: Mauricio Ribeiro <0f77808e58545ae2902769fbb485ffaf122ea8a5@instructure.com>

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