Bump gds-sso to 9.3.0

This is to fix an issue with transfer ot bearer tokens. See
https://github.com/alphagov/signonotron2/pull/245 for details.
Remove redundant gemfury source

we're not using any gems hosted here any more.
Remove pinning of faraday.

Jenkins shouldn't be resolving dependencies as we've checked in the
Gemfile.lock.
Merge pull request #92 from alphagov/bump_gds-sso

Bump gds-sso to 9.3.0