message: Fix boost::format syntax is unsupported on old version
diff: @@ -46,7 +46,7 @@ CWalletTx TxBuilder::Build(const std::vector<CRecipient>& recipients, CAmount& f
  auto& recipient = recipients[i];
  if (recipient.nAmount < 0) {
  - throw std::invalid_argument(boost::str(boost::format(_("Recipient %zu has negative amount")) % i));
  + throw std::invalid_argument(boost::str(boost::format(_("Recipient %1% has negative amount")) % i));
  }
  spend += recipient.nAmount;
  @@ -117,7 +117,7 @@ CWalletTx TxBuilder::Build(const std::vector<CRecipient>& recipients, CAmount& f
  CTxOut vout(recipient.nAmount, recipient.scriptPubKey);
  if (vout.IsDust(minRelayTxFee)) {
  - throw std::invalid_argument(boost::str(boost::format(_("Amount for recipient %zu is too small")) % i));
  + throw std::invalid_argument(boost::str(boost::format(_("Amount for recipient %1% is too small")) % i));
  }
  tx.vout.push_back(vout);
  