Missing plural keys: minor optimization

Refs #309
Refs #310

lib/i18n/tasks/missing_keys.rb

@@ -56,20 +56,21 @@ def missing_used_forest(locales, _base = base_locale)
       end
     end
 
-    def missing_plural_forest(locales, _base = base_locale) # rubocop:disable Metrics/AbcSize
+    def missing_plural_forest(locales, _base = base_locale)
       locales.each_with_object(empty_forest) do |locale, tree|
         next unless I18n.exists?(:'i18n.plural.keys', locale)
 
         required_keys = Set.new(I18n.t(:'i18n.plural.keys', locale: locale, resolve: false))
 
         data[locale].leaves.map(&:parent).compact.uniq.each do |node|
-          children     = node.children
-          present_keys = Set.new(children.to_hash.keys.map(&:to_sym))
-          next if !plural_forms?(children) || present_keys.superset?(required_keys)
+          children = node.children
+          next unless plural_forms?(children)
+          present_keys = Set.new(children.map { |c| c.key.to_sym })
+          next if present_keys.superset?(required_keys)
           tree[node.full_key] = node.derive(
-              value: children.to_hash,
-              children: nil,
-              data: node.data.merge(missing_keys: (required_keys - present_keys).to_a)
+            value: children.to_hash,
+            children: nil,
+            data: node.data.merge(missing_keys: (required_keys - present_keys).to_a)
           )
         end