(maint) - remove github_changelog_generator gem

Author: jordanbreen28

Gemfile

@@ -34,7 +34,6 @@ group :development do
   gem "rubocop-performance", '~> 1.16',          require: false
   gem "rubocop-rspec", '~> 2.19',                require: false
   gem "rb-readline", '= 0.5.5',                  require: false, platforms: [:mswin, :mingw, :x64_mingw]
-  gem "github_changelog_generator", '~> 1.15.0', require: false
 end
 group :system_tests do
   gem "puppet_litmus", '~> 1.0', require: false, platforms: [:ruby, :x64_mingw]