chore(deps-dev): update vcr requirement from ~> 3.0, >= 3.0.1 to >= 3.0.1, ~> 4.0

Updates the requirements on [vcr](https://github.com/vcr/vcr) to permit the latest version.
- [Release notes](https://github.com/vcr/vcr/releases)
- [Changelog](https://github.com/vcr/vcr/blob/master/CHANGELOG.md)
- [Commits](vcr/vcr@v3.0.1...v4.0.0)

Author: dependabot-preview[bot]

flat_api.gemspec

@@ -34,7 +34,7 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency 'json', '~> 2.1', '>= 2.1.0'
 
   s.add_development_dependency 'rspec', '~> 3.6', '>= 3.6.0'
-  s.add_development_dependency 'vcr', '~> 3.0', '>= 3.0.1'
+  s.add_development_dependency 'vcr', '>= 3.0.1', '~> 4.0'
   s.add_development_dependency 'webmock', '~> 1.24', '>= 1.24.3'
   s.add_development_dependency 'autotest', '~> 4.4', '>= 4.4.6'
   s.add_development_dependency 'autotest-rails-pure', '~> 4.1', '>= 4.1.2'