Fix features in libfxrecord for tokio

Adding these missing features allows `cargo test -p libfxrecord` to run
successfully.

libfxrecord/Cargo.toml

@@ -16,7 +16,7 @@ slog-term = "2.5.0"
 structopt = "0.3.14"
 thiserror = "1.0.20"
 toml = "0.5.6"
-tokio = { version = "0.2.21", features = ["tcp", "macros"] }
+tokio = { version = "0.2.21", features = ["io-util", "macros", "rt-threaded", "tcp"] }
 tokio-util = { version = "0.3.1", features = ["codec"] }
 tokio-serde = { version = "0.6.1", features = ["json"] }