Update highline requirement from ~> 2.0 to >= 2, < 4 in /sample

Updates the requirements on [highline](https://github.com/JEG2/highline) to permit the latest version.
- [Changelog](https://github.com/JEG2/highline/blob/master/Changelog.md)
- [Commits](JEG2/highline@v2.0.0...v3.0.0)

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

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

core/spree_core.gemspec

@@ -40,7 +40,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'carmen', '>= 1.0'
   s.add_dependency 'cancancan', '~> 3.2'
   s.add_dependency 'friendly_id', '~> 5.2', '>= 5.2.1'
-  s.add_dependency 'highline', '~> 2.0' # Necessary for the install generator
+  s.add_dependency 'highline', '>= 2', '< 4' # Necessary for the install generator
   s.add_dependency 'kaminari', '~> 1.2'
   s.add_dependency 'money', '~> 6.13'
   s.add_dependency 'monetize', '~> 1.9'