Skip primary key in a more reliable way across rails versions

Rails decided to remove Column#primary [1] and this breaks our ability
to detect whether the column is the primary key as we used to, so rely
on the target class' primary key method for that, which should work fine
in all other rails versions.

[1]
rails/rails@05dd3df

lib/i18n_alchemy/proxy.rb

@@ -69,7 +69,7 @@ def active_record_compatible?
       def build_attributes
         @target_class.columns.each do |column|
           column_name = column.name
-          next if column.primary || column_name.ends_with?("_id") || @localized_attributes.key?(column_name)
+          next if skip_column?(column_name)
 
           parser = detect_parser_from_column(column)
           build_attribute(column_name, parser)
@@ -142,6 +142,12 @@ def detect_parser(type_or_parser)
           type_or_parser
         end
       end
+
+      def skip_column?(column_name)
+        column_name == @target_class.primary_key ||
+          column_name.ends_with?("_id") ||
+          @localized_attributes.key?(column_name)
+      end
     end
   end
 end