Use tokio instead of async-std (#495)

* examples: Use tokio instead of std async

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* test-runtime: Use tokio instead of std async

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* subxt: Use tokio instead of std async

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* examples: Use only necessary tokio features

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

test-runtime/Cargo.toml

@@ -11,5 +11,5 @@ codec = { package = "parity-scale-codec", version = "3.0.0", default-features =
 [build-dependencies]
 subxt = { path = "../subxt" }
 sp-core = "6.0.0"
-async-std = { version = "1.9.0", features = ["attributes", "tokio1"] }
+tokio = { version = "1.8", features = ["rt", "macros"] }
 which = "4.2.2"

test-runtime/build.rs

@@ -38,7 +38,7 @@ use subxt::rpc::{
 
 static SUBSTRATE_BIN_ENV_VAR: &str = "SUBSTRATE_NODE_PATH";
 
-#[async_std::main]
+#[tokio::main]
 async fn main() {
     run().await;
 }