Don't use handler as the IO name

src/kemal/common_log_handler.cr

@@ -1,22 +1,21 @@
 module Kemal
   # Kemal::CommonLogHandler uses STDOUT by default and handles the logging of request/response process time.
   class CommonLogHandler < Kemal::BaseLogHandler
-    @handler : IO
+    @io : IO
 
-    def initialize(io : IO = STDOUT)
-      @handler = io
+    def initialize(@io : IO = STDOUT)
     end
 
     def call(context : HTTP::Server::Context)
       time = Time.now
       call_next(context)
       elapsed_text = elapsed_text(Time.now - time)
-      @handler << time << " " << context.response.status_code << " " << context.request.method << " " << context.request.resource << " " << elapsed_text << "\n"
+      @io << time << " " << context.response.status_code << " " << context.request.method << " " << context.request.resource << " " << elapsed_text << "\n"
       context
     end
 
     def write(message : String)
-      @handler << message
+      @io << message
     end
 
     private def elapsed_text(elapsed)