Use Hash.to_h to construct a new hash

Also declares stringify_keys as a private API method.

lib/rspec-puppet-facts.rb

@@ -179,8 +179,9 @@ def on_supported_os_implementation(opts = {})
     os_facts_hash
   end
 
+  # @api private
   def stringify_keys(hash)
-    Hash[hash.collect { |k,v| [k.to_s, v.is_a?(Hash) ? stringify_keys(v) : v] }]
+    hash.to_h { |k, v| [k.to_s, v.is_a?(Hash) ? stringify_keys(v) : v] }
   end
 
   # Register a custom fact that will be included in the facts hash.

spec/rspec_puppet_facts_spec.rb

@@ -7,6 +7,10 @@
     'spec/fixtures/metadata.json'
   end
 
+  describe '.stringify_keys' do
+    it { expect(described_class.stringify_keys({ os: { family: 'RedHat' } })).to eq({ 'os' => { 'family' => 'RedHat' } }) }
+  end
+
   describe '.facter_version_for_puppet_version' do
     subject(:facter_version) do
       described_class.facter_version_for_puppet_version(puppet_version)