bump ffi to 1.13.1
bump ffi to 1.13.1

https://github.com/ffi/ffi/blob/1.13.1/CHANGELOG.md

refs FOO-1219
flag = none
test plan: specs pass

Change-Id: I01b3c8bdf1287b10f35e0889d914b4f7d164705b
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/252971
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>
QA-Review: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>
Product-Review: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>

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