fbtrace_id is not passed correctly to Koala::Error

[ylecuyer]

I have noticed that facebook changed the format of the error sent to us.

Previously it was x-fb-trace-id
https://github.com/arsduo/koala/blob/master/lib/koala/errors.rb#L66
And now it is fbtrace_id

Example:

"{"error":{"message":"(#613) Calls to this api have exceeded the rate limit.","type":"OAuthException","code":613,"fbtrace_id":"ALBaekPexkW"}}"

it doesn't have the x-fb-debug and x-fb-rev so I'm not sure if they still exist