Update to rspec-rails & rspec supporting rake 12.0

Created by: dmargery

Hello,

following my investigations of bug #8196, I discovered that while we stay with rspec2.6, we can't upgrade to rake >= 11.0.1

In this PR, I've updated rspec-rails and rails and updated the tests to handle the new version of rspec.

To complete the PR, all tests should migrate to the expect().to syntax rather than the .should syntax if we want to avoid deprecation warnings.

@f-didier : do you have many branches of the code with new tests that would also need migrated ?

David