`test_relay_fee` is broken or flaky

[tnull]

Just got this CI failure over at #183:

failures:

---- raw_client::test::test_relay_fee stdout ----

thread 'raw_client::test::test_relay_fee' (4536) panicked at src/raw_client.rs:1252:9:
assertion `left == right` failed
  left: 1e-6
 right: 1e-5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    raw_client::test::test_relay_fee

test result: FAILED. 27 passed; 1 failed; 17 ignored; 0 measured; 0 filtered out; finished in 1.68s

[ValuedMammal]

Fixed by #183.