bump ruby-saml-mod to 0.1.25

fixes CNVS-10695

Change-Id: I76842f9f165d7446de1c32521755d789b11cda25
Reviewed-on: https://gerrit.instructure.com/31851
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Tested-by: Brian Palmer <brianp@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>