Add Ruby 3.1 to CI (#558)

* Add Ruby 3.1 to CI

Update Rubocop for recent Rubies
Disable Rubocop run for Rubies before Ruby 2.4
Quote '3.0' in the CI configuration to ensure it loads a 3.0.x Ruby
Set RUBYOPT="--disable_error_highlight" so Ruby 3.1 error matchers pass

* Add CHANGELOG.md entry

* Re-add deleted line from CHANGELOG.md

* Set minimum supported Ruby version to 2.4.

Remove a number of code bits designed to support Rubies below version 2.4

* Bump version.  Remove unneeded require from Gemfile.  Add require to spec/support file

3 files changed, 11 insertions, 22 deletions

diff --git a/lib/hashie/extensions/coercion.rb b/lib/hashie/extensions/coercion.rb
index a12490a..37d2d7c 100644
--- a/lib/hashie/extensions/coercion.rb
+++ b/lib/hashie/extensions/coercion.rb
@@ -17,14 +17,7 @@ module Hashie
       }.freeze
 
       ABSTRACT_CORE_TYPES =
-        if RubyVersion.new(RUBY_VERSION) >= RubyVersion.new('2.4.0')
-          { Numeric => [Integer, Float, Complex, Rational] }
-        else
-          {
-            Integer => [Fixnum, Bignum],
-            Numeric => [Fixnum, Bignum, Float, Complex, Rational]
-          }
-        end
+        { Numeric => [Integer, Float, Complex, Rational] }
 
       def self.included(base)
         base.send :include, InstanceMethods
diff --git a/lib/hashie/mash.rb b/lib/hashie/mash.rb
index d5cb308..21bcadb 100644
--- a/lib/hashie/mash.rb
+++ b/lib/hashie/mash.rb
@@ -322,22 +322,18 @@ module Hashie
       self.class.new(other_hash).merge(self)
     end
 
-    with_minimum_ruby('2.3.0') do
-      def dig(*keys)
-        super(*keys.map { |key| convert_key(key) })
-      end
+    def dig(*keys)
+      super(*keys.map { |key| convert_key(key) })
     end
 
-    with_minimum_ruby('2.4.0') do
-      def transform_values(&blk)
-        self.class.new(super(&blk))
-      end
+    def transform_values(&blk)
+      self.class.new(super(&blk))
+    end
 
-      # Returns a new instance of the class it was called on, with nil values
-      # removed.
-      def compact
-        self.class.new(super)
-      end
+    # Returns a new instance of the class it was called on, with nil values
+    # removed.
+    def compact
+      self.class.new(super)
     end
 
     with_minimum_ruby('2.5.0') do
diff --git a/lib/hashie/version.rb b/lib/hashie/version.rb
index 1c97af1..d19e3fe 100644
--- a/lib/hashie/version.rb
+++ b/lib/hashie/version.rb
@@ -1,3 +1,3 @@
 module Hashie
-  VERSION = '5.0.1'.freeze
+  VERSION = '5.1.0'.freeze
 end