bump ruby-saml-mod to v0.1.24

Change-Id: I3ad8b91b0138259c4f18f6e456753c75d2c5073e
Reviewed-on: https://gerrit.instructure.com/29513
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Paul Hinze <paulh@instructure.com>
Product-Review: Paul Hinze <paulh@instructure.com>
QA-Review: Paul Hinze <paulh@instructure.com>