Update dependencies (still branch)

[mvz]

Summary

Update some dependencies

Details

Updates dependencies on kramdown and childprocess

Motivation and Context

The dependency on childprocess is most important, because it affects users. Loosening our dependency on childprocess will allow them to use the latest childprocess in their projects. The update of kramdown is just nice for Aruba developers.

How Has This Been Tested?

The update of kramdown was tested by running yardoc. That lead to a change in the Gemfile to explicitely depend on yard, since otherwise its presence in the bundle is only accidental. The change in the dependency on childprocess will be tested by 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.

[olleolleolle]

This is a thoughtful addition.