Fixed a compatibility issue w/ Faraday using Net::HTTP adapter

Fixed a compatibility issue w/ Faraday using Net::HTTP adapter. Faraday creates a Net::HTTPGenericRequest directly (at https://github.com/lostisland/faraday/blob/master/lib/faraday/adapter/net_http.rb#L55), which does not have a ::METHOD constant defined, so we have to use #method to get the HTTP method name.