Update to work on Ruby 2.2.0
Update to work on Ruby 2.2.0

`rb_thread_blocking_region` no longer exists in Ruby 2.2.0. Instead, use
`rb_thread_call_without_gvl`, which has been in Ruby for a while.

Confirmed to work on these MRI Ruby versions:

* 2.2.0
* 2.1.5
* 1.9.3

georgi/audite,GBuella/audite,georgi/audite,GBuella/audite