Revert "Add github_changelog_generator gem"

This reverts commit 8a3516d.

Not compatible with Ruby 2.4 (Puppet 5)...

Author: baurmatt

.sync.yml

@@ -2,8 +2,3 @@
 spec/spec_helper.rb:
   mock_with: ':rspec'
   coverage_report: true
-Gemfile:
-  required:
-    ':release':
-      - gem: github_changelog_generator
-        git: https://github.com/github-changelog-generator/github-changelog-generator

Gemfile

@@ -29,9 +29,6 @@ group :development do
   gem "puppet-module-win-default-r#{minor_version}", '~> 0.4',   require: false, platforms: [:mswin, :mingw, :x64_mingw]
   gem "puppet-module-win-dev-r#{minor_version}", '~> 0.4',       require: false, platforms: [:mswin, :mingw, :x64_mingw]
 end
-group :release do
-  gem "github_changelog_generator", require: false, git: 'https://github.com/github-changelog-generator/github-changelog-generator'
-end
 
 puppet_version = ENV['PUPPET_GEM_VERSION']
 facter_version = ENV['FACTER_GEM_VERSION']