Update SAML dependency to support RSA PKCS#1 v1.5
Created by: beyang
Dependency commit: https://github.com/sourcegraph/gosaml2/commit/f05918046bab66c922c230dde63b91fd0378d979
Merging this w/o CR from @sourcegraph/core-services because:
- Change seems minor and safe
- Would like to get patch to customer in timely manner
- No clear person on the team to review a SAML-related change
cc @sourcegraph/core-services