travis run: https://travis-ci.org/bitcoin/bitcoin/jobs/406813397

```
rpc_psbt.py failed, Duration: 4 s
stdout:
2018-07-22T13:28:57.765000Z TestFramework (INFO): Initializing test directory /tmp/bitcoin_test_runner_20180722_132530/rpc_psbt_49
2018-07-22T13:29:00.531000Z TestFramework (ERROR): Assertion failed
Traceback (most recent call last):
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/test_framework/test_framework.py", line 160, in main
    self.run_test()
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/rpc_psbt.py", line 101, in run_test
    assert_raises_rpc_error(-22, "TX decode failed", self.nodes[0].converttopsbt, signedtx['hex'])
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/test_framework/util.py", line 105, in assert_raises_rpc_error
    assert try_rpc(code, message, fun, *args, **kwds), "No exception raised"
AssertionError: No exception raised
"                         marked bip-125 replaceable. If true, the sequence numbers in the transaction will\n"
            "                         be left unchanged from the original. If false, any input sequence numbers in the\n"
            "                         original transaction that were less than 0xfffffffe will be increased to 0xfffffffe\n"
            "                         so the new transaction will not be explicitly bip-125 replaceable (though it may\n"
            "                         still be replaceable in practice, for example if it has unconfirmed ancestors which\n"
            "                         are replaceable)."},
                            {"estimate_mode", RPCArg::Type::STR,  "UNSET", "The fee estimate mode, must be one of:\n"
            "         \"UNSET\"\n"
            "         \"ECONOMICAL\"\n"
            "         \"CONSERVATIVE\""},
                        },
                        "options"},
                },
                RPCResult{
            "{\n"
            "  \"txid\":    \"value\",   (string)  The id of the new transaction\n"
            "  \"origfee\":  n,         (numeric) Fee of the replaced transaction\n"
            "  \"fee\":      n,         (numeric) Fee of the new transaction\n"
            "  \"errors\":  [ str... ] (json array of strings) Errors encountered during processing (may be empty)\n"
            "}\n"
                },
                RPCExamples{
            "\nBump the fee, get the new transaction\'s txid\n" +
                    HelpExampleCli("bumpfee", "<txid>")
                },
            }.ToString());
    }
    RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VOBJ});
    uint256 hash(ParseHashV(request.params[0], "txid"));