Use "replaceable" instead of "rbfoptin" in bitcoin-tx.

To be consistent with RPC naming

src/bitcoin-tx.cpp

@@ -77,7 +77,7 @@ static int AppInitRawTx(int argc, char* argv[])
         strUsage += HelpMessageOpt("in=TXID:VOUT(:SEQUENCE_NUMBER)", _("Add input to TX"));
         strUsage += HelpMessageOpt("locktime=N", _("Set TX lock time to N"));
         strUsage += HelpMessageOpt("nversion=N", _("Set TX version to N"));
-        strUsage += HelpMessageOpt("rbfoptin(=N)", _("Set RBF opt-in sequence number for input N (if not provided, opt-in all available inputs)"));
+        strUsage += HelpMessageOpt("replaceable(=N)", _("Set RBF opt-in sequence number for input N (if not provided, opt-in all available inputs)"));
         strUsage += HelpMessageOpt("outaddr=VALUE:ADDRESS", _("Add address-based output to TX"));
         strUsage += HelpMessageOpt("outpubkey=VALUE:PUBKEY[:FLAGS]", _("Add pay-to-pubkey output to TX") + ". " +
             _("Optionally add the \"W\" flag to produce a pay-to-witness-pubkey-hash output") + ". " +
@@ -673,7 +673,7 @@ static void MutateTx(CMutableTransaction& tx, const std::string& command,
         MutateTxVersion(tx, commandVal);
     else if (command == "locktime")
         MutateTxLocktime(tx, commandVal);
-    else if (command == "rbfoptin") {
+    else if (command == "replaceable") {
         MutateTxRBFOptIn(tx, commandVal);
     }