bump ffi to resolve build error on Ubuntu
bump ffi to resolve build error on Ubuntu

flag = none

Test plan:
• run `bundle install`
• run `bundle exec rails canvas:compile_assets
• verify no errors related to commit message

Change-Id: Ifff4a6c32bf517b35a6981bb14a17b159368ff9b
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/284109
Reviewed-by: Andrea Cirulli <b4e55ef5ee4bae8ad31f7c81009bfc0af1714a1f@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>
Product-Review: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>

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