Less verbose rate limit messages from git_immersion.feature

- Includes pull request https://github.com/AgileVentures/AutoGraderExamples/pull/19, which inlcludes https://github.com/AgileVentures/AutoGraderExamples/pull/18
- Reworded messages
- Left the print of warnings from mvp_spec here, might still be too much during pull request builds: https://github.com/apelade/AutoGraderExamples/blob/026fbcbee543a6c1e06639713203bb86cd30191c/features/step_definitions/git_immersion_testing_steps.rb#L15