update async-std to 1.6.0

Author: yoshuawuyts

Cargo.toml

@@ -25,7 +25,7 @@ async_std = [] # "async-std" when it is not default
 [dependencies]
 # Note(yoshuawuyts): used for async_std's `channel` only; use "core" once possible.
 # features: async_std
-async-std = { version = "1.4.0", features = ["unstable"] }
+async-std = { version = "1.6.0", features = ["unstable"] }
 
 # features: hyperium/http
 http = { version = "0.2.0", optional = true }
@@ -42,4 +42,4 @@ serde_urlencoded = "0.6.1"
 
 [dev-dependencies]
 http = "0.2.0"
-async-std = { version = "1.4.0", features = ["unstable", "attributes"] }
+async-std = { version = "1.6.0", features = ["unstable", "attributes"] }