Update danger-changelog requirement from ~> 0.6.0 to ~> 0.7.0

Updates the requirements on [danger-changelog](https://github.com/dblock/danger-changelog) to permit the latest version.
- [Release notes](https://github.com/dblock/danger-changelog/releases)
- [Changelog](https://github.com/dblock/danger-changelog/blob/master/CHANGELOG.md)
- [Commits](dblock/danger-changelog@v0.6.0...v0.7.0)

---
updated-dependencies:
- dependency-name: danger-changelog
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile

@@ -21,7 +21,7 @@ group :development, :test do
 end
 
 group :test do
-  gem 'danger-changelog', '~> 0.6.0'
+  gem 'danger-changelog', '~> 0.7.0'
   gem 'danger-toc', '~> 0.2.0'
   gem 'minitest'
   gem 'mocha'