fix: Update echo_server to new listen API (#625)

examples/echo_server.ts

@@ -1,12 +1,9 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-const { listen, copy } = Deno;
-
-(async (): Promise<void> => {
-  const addr = "0.0.0.0:8080";
-  const listener = listen("tcp", addr);
-  console.log("listening on", addr);
-  while (true) {
-    const conn = await listener.accept();
-    copy(conn, conn);
-  }
-})();
+const hostname = "0.0.0.0";
+const port = 8080;
+const listener = Deno.listen({ hostname, port });
+console.log(`Listening on ${hostname}:${port}`);
+while (true) {
+  const conn = await listener.accept();
+  Deno.copy(conn, conn);
+}