Release 0.6.0

Bump rubocop dependency to 0.50 to stay current with the community

• rubocop 0.50 release notes https://github.com/bbatsov/rubocop/releases/tag/v0.50.0

Disable Style/Lambda Cop

• Discussion #27
• Definition https://rubocop.readthedocs.io/en/latest/cops_style/#stylelambda