Log Message:
Update ruby-childprocess to 0.5.5.

* Longer sleep (increase stability but won't affect runtime).
* Work around JRuby problem.
* Spec environment unset in parent is unset in parent when set in grandparent.
* Remove environment variables not in ENV that are in ProcessBuilder
  environment.
* Remove unnecessary stringification of ENV keys MSP-11414
  Unlike @environment, which is a generic Hash, ENV is guarenteed to be
  <String, String>, so remove the keys #to_s calls for ENV.