Close old logger when rotating, fixes #1008

Changes.md

@@ -1,3 +1,8 @@
+HEAD
+-----------
+
+- log rotation via USR2 didn't close the old logger [#1008]
+
 2.12.4
 -----------
 

lib/sidekiq/logging.rb

@@ -26,9 +26,11 @@ module Sidekiq
     end
 
     def self.initialize_logger(log_target = STDOUT)
+      oldlogger = @logger
       @logger = Logger.new(log_target)
       @logger.level = Logger::INFO
       @logger.formatter = Pretty.new
+      oldlogger.close if oldlogger && !$TESTING # don't want to close testing's STDOUT logging
       @logger
     end