fixup: support older Rust versions

We need to make sure the 'serde_bytes' name is in scope.

src/deserializer.rs

@@ -754,7 +754,7 @@ mod tests {
  use std::collections::HashMap;
 
  use serde::de::DeserializeOwned;
- use serde_bytes::ByteBuf;
+ use serde_bytes::{self, ByteBuf};
 
  use byte_record::ByteRecord;
  use error::Error;