Update hdpayload.rs (#153)

- Fix chain-wallet-libs tests after bip39 removal

Author: minikin

src/chain-wallet-libs/hdkeygen/src/rindex/hdpayload.rs

@@ -191,9 +191,10 @@ impl HdKey {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use bip39::SEED_SIZE;
     use ed25519_bip32::XPrv;
 
+    const SEED_SIZE: usize = 64;
+
     fn generate_from_daedalus_seed(bytes: &[u8]) -> XPrv {
         use cryptoxide::mac::Mac;