Update lib/net/http/response.rb

@natematykiewicz's suggestion to avoid a string allocation

Co-authored-by: Nate Matykiewicz <[email protected]>

Author: technicalpickles

lib/net/http/response.rb

@@ -273,7 +273,7 @@ def code_type   #:nodoc:
 
   def error!   #:nodoc:
     message = @code
-    message += " #{@message.dump}" if @message
+    message = "#{message} #{@message.dump}" if @message
     raise error_type().new(message, self)
   end