Day of the month should be zero-padded, not blank-padded

Technically both 1 and 2 digits are allowed, however it seems that Faraday overrides the Date header passed to the server:

date: "Sat,  6 Apr 2013 20:27:46 GMT" (as generated by hmac#sign_request)
date: "Sat, 06 Apr 2013 20:27:46 GMT" (passed along by Faraday)

Hence with query based requests it works, as nothing is overridden by Faraday. With header based requests this fails however.