Update rspec.
Convert to latest RSpec syntax using transept.
Fix deprecated rspec usage.
Upgrade lots of other gems.
Move away from `stub_chain`.
Enforce use of new rspec-mocks syntax.
Update excon.

Excon now includes a default user-agent.
Update typhoeus-old Gemfile.lock as well.
This was Typhoeus::Hydra.stub, not rspec's stub.
Relax excon version check: 0.25 works fine.
Ensure `SPEC_ROOT` is expanded.

Our absolute dir spec depends on this.
Merge pull request #326 from vcr/update_gems

Update gems