Regenerating binstub for rspec-core

This commit fixes this warning:

![old_binstub_for_rspec](https://cloud.githubusercontent.com/assets/80530/4965834/f4c98396-6798-11e4-9a7c-e2039ee4fdc3.png)

And this is after:

![added_new_rspec-core_binstub](https://cloud.githubusercontent.com/assets/80530/4965837/152b4dae-6799-11e4-8e3c-5b084b2730ed.png)