Also upgrade its dependencies. Includes Rails 5 support.

Changelogs:
rspec-rails: https://github.com/rspec/rspec-rails/compare/v3.4.2...v3.5.0
rspec-core: https://github.com/rspec/rspec-core/compare/v3.4.0...v3.5.0
rspec-support: https://github.com/rspec/rspec-support/compare/v3.4.0...v3.5.0
rspec-expectations: https://github.com/rspec/rspec-expectations/compare/v3.4.0...v3.5.0
rspec-mocks: https://github.com/rspec/rspec-mocks/compare/v3.4.0...v3.5.0
rspec: https://github.com/rspec/rspec/compare/v3.4.0...v3.5.0