[Chore] Refactor code

Author: lmduc

Diff for: lib/kafka/consumer.rb

@@ -594,9 +594,9 @@ def clear_current_offsets(excluding: {})
 
     def scan_for_subscribing
       @subscribed_topics.each do |topic_or_regex, config|
-        default_offset = config[:default_offset]
-        start_from_beginning = config[:start_from_beginning]
-        max_bytes_per_partition = config[:max_bytes_per_partition]
+        default_offset = config.fetch(:default_offset)
+        start_from_beginning = config.fetch(:start_from_beginning)
+        max_bytes_per_partition = config.fetch(:max_bytes_per_partition)
         if topic_or_regex.is_a?(Regexp)
           subscribe_to_regex(topic_or_regex, default_offset, start_from_beginning, max_bytes_per_partition)
         else