return `Observable` instead of `Single`; send `Error` if the response has one
return `Observable` instead of `Single`; send `Error` if the response has one

bontoJR/RxAlamofire,bontoJR/RxAlamofire,RxSwiftCommunity/RxAlamofire,RxSwiftCommunity/RxAlamofire,RxSwiftCommunity/RxAlamofire