Update warning requirement from ~> 1.3.0 to ~> 1.4.0

Updates the requirements on [warning](https://github.com/jeremyevans/ruby-warning) to permit the latest version.
- [Changelog](https://github.com/jeremyevans/ruby-warning/blob/master/CHANGELOG)
- [Commits](jeremyevans/ruby-warning@1.3.0...1.4.0)

---
updated-dependencies:
- dependency-name: warning
  dependency-type: direct:development
...

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

Gemfile

@@ -26,5 +26,5 @@ end
 
 group(:test) do
   gem('test-unit', '~> 3.6.2')
-  gem('warning', '~> 1.3.0')
+  gem('warning', '~> 1.4.0')
 end