Fix merkledb compilation as independent module
@@ -16,7 +16,8 @@ use std::fmt::Debug;
use hex::FromHex;
use rand::{thread_rng, Rng, RngCore};
-use serde::Serialize;
+use serde::ser::Serialize;
+use serde_derive::Serialize;
use serde_json::{from_str, to_string};
use exonum_crypto::Hash;
