Invoke HashWithIndifferentAccess#to_hash to cast to a hash since #to_h is not defined on Ruby19 and lower

lib/paper_trail/has_paper_trail.rb

@@ -294,7 +294,7 @@ module PaperTrail
       def changes_for_paper_trail
         self.changes.delete_if do |key, value|
           !notably_changed.include?(key)
-        end.tap { |changes| self.class.serialize_attribute_changes(changes) }.to_h
+        end.tap { |changes| self.class.serialize_attribute_changes(changes) }.to_hash
       end
 
       # Invoked via`after_update` callback for when a previous version is reified and then saved

spec/models/version_spec.rb

@@ -21,7 +21,7 @@ describe PaperTrail::Version, :type => :model do
         specify { expect(PaperTrail.serializer).to be PaperTrail::Serializers::YAML }
 
         it "should store out as a plain hash" do
-          expect(value =~ /ActiveSupport::HashWithIndifferentAccess/).to be_nil
+          expect(value =~ /HashWithIndifferentAccess/).to be_nil
         end
       end
 
@@ -29,7 +29,7 @@ describe PaperTrail::Version, :type => :model do
         before(:all) { PaperTrail.serializer = PaperTrail::Serializers::JSON }
 
         it "should store out as a plain hash" do
-          expect(value =~ /ActiveSupport::HashWithIndifferentAccess/).to be_nil
+          expect(value =~ /HashWithIndifferentAccess/).to be_nil
         end
 
         after(:all) { PaperTrail.serializer = PaperTrail::Serializers::YAML }