upgrade async-std to 1.6

Signed-off-by: Hexilee <i@hexilee.me>

Author: Hexilee

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "async-postgres"
-version = "0.5.0"
+version = "0.5.1"
 authors = ["Hexilee <i@hexilee.me>"]
 edition = "2018"
 license = "MIT"
@@ -21,19 +21,19 @@ codecov = { repository = "Hexilee/async-postgres" }
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-bytes = "0.5.3"
-tokio-postgres = { version = "0.5.2", default-features = false }
-tokio = "0.2.14"
-async-std = "1.5"
-futures = { version = "0.3.4", default-features = false }
+bytes = "0.5"
+tokio-postgres = { version = "0.5", default-features = false }
+tokio = "0.2"
+async-std = "1.6"
+futures = { version = "0.3", default-features = false }
 
 
 [dev-dependencies]
-async-std = { version = "1.5", features = ["attributes"] }
-tokio = { version = "0.2.14", features = ["full"] }
-tokio-postgres = "0.5.3"
-postgres-native-tls = "0.3.0"
-native-tls = "0.2.4"
+async-std = { version = "1.6", features = ["attributes"] }
+tokio = { version = "0.2", features = ["full"] }
+tokio-postgres = "0.5"
+postgres-native-tls = "0.3"
+native-tls = "0.2"
 
 [features]
 docs = ["full"]