RSpec3!

Obsoletes #232.

Upgraded to rspec. Transpec did 99% of the work, but I fixed a few other issues. There is an annoying error message that I haven't figured out, but it doesn't isn't causing any tests to fail:

```
An error occurred in an `after(:context)` hook.
  RuntimeError: let declaration `data` accessed in an `after(:context)` hook at:
  /Users/Thoughtworker/repos/travis-ci/travis-build/spec/spec_helper.rb:66:in `store_example'

`let` and `subject` declarations are not intended to be called
in an `after(:context)` hook, as they exist to define state that
is reset between each example, while `after(:context)` exists to
cleanup state that is shared across examples in an example group.

  occurred at /opt/boxen/rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-3.0.0/lib/rspec/core/memoized_helpers.rb:155:in `fetch'
```