Using Spring was hiding an loading error. When you start Rspec, Rails
and its engines are not loaded yet. So our way to load the spec helper
via `Rails.root` did not work when you ran specs on their own without
loading Rails with Spring first.
This is work in progress. The DFC Connector uses a more recent DFC
version and other endpoints still use the old serializers. We need to
update those endpoints as well and update the version number in the API
URL.
