Inject STDOUT by default in CommonLogHandler

src/kemal/common_log_handler.cr

@@ -2,7 +2,7 @@ module Kemal
   class CommonLogHandler < Kemal::BaseLogHandler
     @handler : IO
 
-    def initialize(io : IO)
+    def initialize(io : IO = STDOUT)
       @handler = io
     end
 

src/kemal/config.cr

@@ -74,7 +74,7 @@ module Kemal
 
     private def setup_log_handler
       @logger ||= if @logging
-                    Kemal::CommonLogHandler.new(STDOUT)
+                    Kemal::CommonLogHandler.new
                   else
                     Kemal::NullLogHandler.new
                   end