Update dependencies

Rails 4.1.5 for latest release

Personal version of rspec-sequel-matchers to fix issue with not using
rails inflections per
https://github.com/openhood/rspec_sequel_matchers/pull/12
Have descriptor class names closer to SAML spec

By using rails inflections (as suggested by @smangelsdorf) our
descriptor class naming changes from IdpSsoDescriptor to the sane IDPSSODescriptor without breaking acronyms for class names commonly used by Rails, Sequel, FactoryGirl and others.