Update dependency github_changelog_generator to '~> 1.18.0' (#75)

Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

Gemfile

@@ -29,5 +29,5 @@ group :integration do
 end
 
 group :tools do
-  gem 'github_changelog_generator', '~> 1.17.0'
+  gem 'github_changelog_generator', '~> 1.18.0'
 end