Fix omniauth-shibboleth-redux
Adds require: 'omniauth-shibboleth'
to omniauth-shibboleth-redux line in Gemfile,
otherwise the Omniauth Strategy Loader fails to find the Shibboleth Strategy.
See https://www.rubydoc.info/gems/omniauth-shibboleth-redux/2.0.0#install
gem 'omniauth-shibboleth-redux', require: 'omniauth-shibboleth'
This is a fix for !121235 (merged).