Remove support for versions of ruby prior to 2.6

Ruby 2.5 and earlier are all EOL and are no longer receiving security
updates.

Signed-off-by: Marc A. Paradise <marc.paradise@gmail.com>

.expeditor/verify.pipeline.yml

@@ -11,29 +11,13 @@ expeditor:
 
 steps:
 
-- label: run-lint-ruby-2.4
+- label: run-lint-ruby-2.6
   command:
     - .expeditor/run_linux_tests.sh rake style
   expeditor:
     executor:
       docker:
-        image: ruby:2.4
-
-- label: run-specs-ruby-2.4
-  command:
-    - .expeditor/run_linux_tests.sh rake
-  expeditor:
-    executor:
-      docker:
-        image: ruby:2.4
-
-- label: run-specs-ruby-2.5
-  command:
-    - .expeditor/run_linux_tests.sh rake
-  expeditor:
-    executor:
-      docker:
-        image: ruby:2.5
+        image: ruby:2.6
 
 - label: run-specs-ruby-2.6
   command:

Gemfile

@@ -2,22 +2,14 @@ source "https://rubygems.org"
 
 gemspec
 
-gem "chef-utils", "= 16.6.14" if RUBY_VERSION < "2.6.0"
-
 group :test do
   gem "rake"
   gem "rspec"
   gem "webrick"
   gem "webmock", "~> 3.4"
   gem "contracts", "~> 0.16.0" # this entry can go away when ruby < 3 support is gone
-  if RUBY_VERSION < "2.6.0"
-    gem "climate_control", "= 0.1.0"
-    gem "vcr", "= 6.0.0"
-    gem "mixlib-shellout", "= 3.2.5"
-  else
-    gem "climate_control", "~> 1.0"
-    gem "vcr"
-  end
+  gem "climate_control", "~> 1.0"
+  gem "vcr"
 end
 
 # use old chefstyle to support TargetRubyVersion of 1.9

README.md

@@ -12,8 +12,9 @@
 
 ## Supports
 
-- Ruby 1.9.3+
-- Chef 11.6.2+ chef-client upgrades
+- Ruby 2.6+
+- Chef 14+ chef-client upgrades
+  - To upgrade older versions of chef-client, it will be necessary to use older versions of mixlib-install that are compatible with versions of ruby prior to 2.6.
 
 ## Command Line Usage
 ```

mixlib-install.gemspec

@@ -16,7 +16,7 @@ Gem::Specification.new do |spec|
   spec.files         = %w{LICENSE Gemfile Rakefile} + Dir.glob("*.gemspec") + Dir.glob("{bin,lib,support}/**/*")
   spec.executables   = ["mixlib-install"]
   spec.require_paths = ["lib"]
-
+  spec.required_ruby_version = ">= 2.6.0"
   spec.add_dependency "mixlib-shellout"
   spec.add_dependency "mixlib-versioning"
   spec.add_dependency "thor"