Log Message:
Update ruby-pathname2 to 1.8.0.

== 1.8.0 - 19-Jun-2016
* Changed license to Apache 2.0.
* Some cleanup and updates to the Rakefile and benchmarks.
* Refactored some realpath tests so they're not touching system files like
  /dev/stdin any more. Thanks go to Michael R. Crusoe for pointing out the
  potential pitfalls of doing that.