minor fix due to ObjectMapper removal, this fix is blocked by PR https://github.com/readium/r2-shared-swift/pull/42
minor fix due to ObjectMapper removal, this fix is blocked by PR https://github.com/readium/r2-shared-swift/pull/42

readium/r2-streamer-swift,readium/r2-streamer-swift,readium/r2-streamer-swift,readium/r2-streamer-swift,readium/r2-streamer-swift