Odd issue when attempting to gem install hammertime on ruby 2.3.4p301 using RubyGems 2.6.14.
$ gem install hammertime
ERROR: Could not find a valid gem 'ruby-debug-base' (~> 0.10.6.0) in any repository
ERROR: Possible alternatives: ruby-debug-base
The gem is probably untested on those considering #1 but I thought it might be worth letting you know. I couldn't find an obvious reason for this while looking at the gemspec.