Update gitlab requirement from ~> 4.0 to >= 4, < 6

Updates the requirements on [gitlab](https://github.com/NARKOZ/gitlab) to permit the latest version.
- [Release notes](https://github.com/NARKOZ/gitlab/releases)
- [Commits](NARKOZ/gitlab@v4.0.0...v5.0.0)

---
updated-dependencies:
- dependency-name: gitlab
  dependency-type: direct:production
...

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

Author: dependabot[bot]

modulesync.gemspec

@@ -26,7 +26,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'voxpupuli-rubocop', '~> 2.8.0'
 
   spec.add_runtime_dependency 'git', '~>1.7'
-  spec.add_runtime_dependency 'gitlab', '~>4.0'
+  spec.add_runtime_dependency 'gitlab', '>=4', '<6'
   spec.add_runtime_dependency 'octokit', '>=4', '<9'
   spec.add_runtime_dependency 'puppet-blacksmith', '>= 3.0', '< 8'
   spec.add_runtime_dependency 'thor', '1.3.0'