Update to Tokio 0.2 (#428)

examples/akamai.rs

@@ -1,3 +1,5 @@
+fn main() {}
+/* TODO: re-enable when tokio-rustls is updated
 use h2::client;
 use http::{Method, Request};
 use tokio::net::TcpStream;
@@ -73,3 +75,4 @@ pub async fn main() -> Result<(), Box<dyn Error>> {
     }
     Ok(())
 }
+*/