Update futures-timer to 0.4

Author: taiki-e

runtime-native/Cargo.toml

@@ -21,7 +21,7 @@ async-datagram = "3.0.0"
 juliex = "0.3.0-alpha.6"
 lazy_static = "1.3.0"
 romio = "0.3.0-alpha.9"
-futures-timer = "0.3.0"
+futures-timer = "0.4.0"
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 futures01 = { package = "futures", version = "0.1" }