Add typhoeus 0.5 dependency.

Typhoeus doesn't add the Faraday adapter used in [Travis::Client::Session](https://github.com/travis-ci/travis/blob/3d5e5f5841955339382278020a6a55c5fc46991a/lib/travis/client/session.rb#L5) until version [0.5.0](https://github.com/typhoeus/typhoeus/compare/v0.4.2...v0.5.0), so the CLI won't run with an older version.