Something in the MRI stdlib test suite (rake test:mri:stdlib) appears to hang when shutting down the test suite. The suite itself runs green, but after the last test completes it appears to intermittently hang and fail to complete, which leads to Travis marking it as a failure.

In 44d0e0c I have moved this suite to allowed failures, but we will want to figure out why this suite sometimes hangs and move it back out.