chore(tutorials): Add another .await after client connect call (#112)

tonic-examples/helloworld-tutorial.md

@@ -266,7 +266,7 @@ The client is much simpler than the server as we don't need to implement any ser
 ```rust
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let mut client = GreeterClient::connect("http://[::1]:50051")?;
+    let mut client = GreeterClient::connect("http://[::1]:50051").await?;
 
     let request = tonic::Request::new(HelloRequest {
         name: "Tonic".into(),