upgrade async-macros to 2.0.0 (#519)

Signed-off-by: Yoshua Wuyts <[email protected]>

Author: yoshuawuyts

Diff for: Cargo.toml

@@ -51,7 +51,7 @@ std = [
 
 [dependencies]
 async-attributes = { version = "1.1.0", optional = true }
-async-macros = { version = "1.0.0", optional = true }
+async-macros = { version = "2.0.0", optional = true }
 async-task = { version = "1.0.0", optional = true }
 broadcaster = { version = "0.2.6", optional = true, default-features = false, features = ["default-channels"] }
 crossbeam-channel = { version = "0.3.9", optional = true }