Update mixlib-shellout requirement from ~> 2.2, < 2.3.0 to ~> 2.2, < 2.5.0

Updates the requirements on [mixlib-shellout](https://github.com/chef/mixlib-shellout) to permit the latest version.
- [Release notes](https://github.com/chef/mixlib-shellout/releases)
- [Changelog](https://github.com/chef/mixlib-shellout/blob/master/CHANGELOG.md)
- [Commits](chef/mixlib-shellout@2.2.0...v2.4.4)

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

Author: dependabot-support

sensu-plugins-redis.gemspec

@@ -45,7 +45,7 @@ Gem::Specification.new do |s| # rubocop:disable Metrics/BlockLength
   s.add_development_dependency 'kitchen-docker',            '~> 2.6'
   s.add_development_dependency 'kitchen-localhost',         '~> 0.3'
   # locked to keep ruby 2.1 support, this is pulled in by test-kitchen
-  s.add_development_dependency 'mixlib-shellout',           ['< 2.3.0', '~> 2.2']
+  s.add_development_dependency 'mixlib-shellout',           '~> 2.2', '< 2.5.0'
   s.add_development_dependency 'pry',                       '~> 0.10'
   s.add_development_dependency 'rake',                      '~> 12.3'
   s.add_development_dependency 'redcarpet',                 '~> 3.2'