Pass &:path as an argument, instead of a block

lib/pronto/formatter/checkstyle_formatter.rb

@@ -25,18 +25,14 @@ def open_xml
       end
 
       def process_messages(messages)
-        group_messages(messages).map do |path, path_messages|
+        messages.group_by(&:path).map do |path, path_messages|
           REXML::Element.new('file', @checkstyle).tap do |file|
             file.attributes['name'] = path
             add_file_messages(path_messages, file)
           end
         end
       end
 
-      def group_messages(messages)
-        messages.group_by { |message| message.path }
-      end
-
       def add_file_messages(path_messages, file)
         path_messages.each do |message|
           REXML::Element.new('error', file).tap do |e|