Upgrade to tokio 1.0.

Cargo.toml

@@ -12,7 +12,7 @@ crossbeam-channel = "0.5.0"
 futures = { version = "0.3.8", default-features = false, features = ["thread-pool"] }
 parking_lot = "0.11.0"
 rand = "0.7.3"
-tokio = { version = "0.3", features = ["rt-multi-thread", "time", "parking_lot"] }
+tokio = { version = "1.0", features = ["rt-multi-thread", "time", "parking_lot"] }
 
 [features]
 default = []