use EventMachine::HttpResponseHeader#raw in example

[takada-s]

examples/http_log.rb is very helpful for me.
I noticed that the response header handling can be more simple by using EventMachine::HttpResponseHeader#raw. (definition here)

[dj2]

This drops the to_http_header() call that the old method is doing.

[takada-s]

in my environment, response_header.raw() returns well-formed hash like this:

resp.response_header:
{"CONTENT_TYPE"=>"text/html",
 "DATE"=>"Fri, 05 Jun 2015 01:01:07 GMT",
 "CONNECTION"=>"close",
 "TRANSFER_ENCODING"=>"chunked"}
resp.response_header.raw:
{"Content-Type"=>"text/html",
 "Date"=>"Fri, 05 Jun 2015 01:01:07 GMT",
 "Connection"=>"close",
 "Transfer-Encoding"=>"chunked"}

( I used pp resp.response_header and pp resp.response_header.raw)