Loosen dependency on childprocess

[mvz]

Summary

Loosen dependency on childprocess

Details

Update dependencies to allow childprocess 3.0. Adjust Gemfile to install newer versions on compatible rubies.

Motivation and Context

Allows downstream projects to update their childprocess dependency.

How Has This Been Tested?

Travis.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (cleanup of codebase without changing any existing functionality)
• Update documentation

Checklist:

• I've added tests for my code
• My change requires a change to the documentation.
• I have updated the documentation accordingly.